RE: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
-Original Message-
From: Alexander Graf [mailto:ag...@suse.de]
Sent: Wednesday, July 24, 2013 1:55 PM
To: “tiejun.chen”
Cc: Bhushan Bharat-R65777; kvm-ppc@vger.kernel.org; k...@vger.kernel.org list;
Wood Scott-B07421; Gleb Natapov; Paolo Bonzini
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel
managed pages
On 24.07.2013, at 04:26, “tiejun.chen” wrote:
On 07/18/2013 06:27 PM, Alexander Graf wrote:
On 18.07.2013, at 12:19, “tiejun.chen” wrote:
On 07/18/2013 06:12 PM, Alexander Graf wrote:
On 18.07.2013, at 12:08, “tiejun.chen” wrote:
On 07/18/2013 05:48 PM, Alexander Graf wrote:
On 18.07.2013, at 10:25, Bhushan Bharat-R65777 wrote:
-Original Message-
From: Bhushan Bharat-R65777
Sent: Thursday, July 18, 2013 1:53 PM
To: ' tiejun.chen '
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood Scott-
B07421
Subject: RE: [PATCH 2/2] kvm: powerpc: set cache coherency only
for kernel managed pages
-Original Message-
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, July 18, 2013 1:52 PM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott-
B07421
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 04:08 PM, Bhushan Bharat-R65777 wrote:
-Original Message-
From: kvm-ppc-ow...@vger.kernel.org
[mailto:kvm-ppc-ow...@vger.kernel.org] On Behalf Of tiejun.chen
Sent: Thursday, July 18, 2013 1:01 PM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott-
B07421
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 03:12 PM, Bhushan Bharat-R65777 wrote:
-Original Message-
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, July 18, 2013 11:56 AM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott- B07421; Bhushan Bharat-R65777
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 02:04 PM, Bharat Bhushan wrote:
If there is a struct page for the requested mapping then
it's normal DDR and the mapping sets M bit (coherent,
cacheable) else this is treated as I/O and we set I +
G (cache inhibited,
guarded)
This helps setting proper TLB mapping for direct assigned
device
Signed-off-by: Bharat Bhushan
bharat.bhus...@freescale.com
---
arch/powerpc/kvm/e500_mmu_host.c | 17 -
1 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kvm/e500_mmu_host.c
b/arch/powerpc/kvm/e500_mmu_host.c
index 1c6a9d7..089c227 100644
--- a/arch/powerpc/kvm/e500_mmu_host.c
+++ b/arch/powerpc/kvm/e500_mmu_host.c
@@ -64,13 +64,20 @@ static inline u32
e500_shadow_mas3_attrib(u32 mas3, int
usermode)
return mas3;
}
-static inline u32 e500_shadow_mas2_attrib(u32 mas2, int
usermode)
+static inline u32 e500_shadow_mas2_attrib(u32 mas2,
+pfn_t pfn)
{
+ u32 mas2_attr;
+
+ mas2_attr = mas2 MAS2_ATTRIB_MASK;
+
+ if (!pfn_valid(pfn)) {
Why not directly use kvm_is_mmio_pfn()?
What I understand from this function (someone can correct
me) is that it
returns false when the page is managed by kernel and is
not marked as RESERVED (for some reason). For us it does not
matter whether the page is reserved or not, if it is kernel
visible page then it
is DDR.
I think you are setting I|G by addressing all mmio pages,
right? If so,
KVM: direct mmio pfn check
Userspace may specify memory slots that are backed by
mmio pages rather than
normal RAM. In some cases it is not enough to identify
these mmio
pages
by pfn_valid(). This patch adds checking the PageReserved as
well.
Do you know what are those some cases and how checking
PageReserved helps in
those cases?
No, myself didn't see these actual cases in qemu,too. But this
should be chronically persistent as I understand ;-)
Then I will wait till someone educate me :)
The reason is , kvm_is_mmio_pfn() function looks pretty heavy and I do
not want to call this for all tlbwe operation unless it is necessary.
It certainly does more than we need and potentially slows down the fast
path (RAM mapping). The only thing it does on top of if (pfn_valid()) is to
check for pages that are declared reserved on the host. This happens in 2
cases:
1) Non cache coherent DMA
2) Memory hot remove
The non coherent DMA case would be interesting, as with the mechanism
as
it is in place in Linux today, we could potentially break normal guest
operation
if we don't take it into account. However, it's Kconfig guarded by:
Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On 24.07.2013, at 11:11, Bhushan Bharat-R65777 wrote:
-Original Message-
From: Alexander Graf [mailto:ag...@suse.de]
Sent: Wednesday, July 24, 2013 1:55 PM
To: “tiejun.chen”
Cc: Bhushan Bharat-R65777; kvm-ppc@vger.kernel.org; k...@vger.kernel.org
list;
Wood Scott-B07421; Gleb Natapov; Paolo Bonzini
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel
managed pages
On 24.07.2013, at 04:26, “tiejun.chen” wrote:
On 07/18/2013 06:27 PM, Alexander Graf wrote:
On 18.07.2013, at 12:19, “tiejun.chen” wrote:
On 07/18/2013 06:12 PM, Alexander Graf wrote:
On 18.07.2013, at 12:08, “tiejun.chen” wrote:
On 07/18/2013 05:48 PM, Alexander Graf wrote:
On 18.07.2013, at 10:25, Bhushan Bharat-R65777 wrote:
-Original Message-
From: Bhushan Bharat-R65777
Sent: Thursday, July 18, 2013 1:53 PM
To: ' tiejun.chen '
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood Scott-
B07421
Subject: RE: [PATCH 2/2] kvm: powerpc: set cache coherency only
for kernel managed pages
-Original Message-
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, July 18, 2013 1:52 PM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott-
B07421
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 04:08 PM, Bhushan Bharat-R65777 wrote:
-Original Message-
From: kvm-ppc-ow...@vger.kernel.org
[mailto:kvm-ppc-ow...@vger.kernel.org] On Behalf Of tiejun.chen
Sent: Thursday, July 18, 2013 1:01 PM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott-
B07421
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 03:12 PM, Bhushan Bharat-R65777 wrote:
-Original Message-
From: tiejun.chen [mailto:tiejun.c...@windriver.com]
Sent: Thursday, July 18, 2013 11:56 AM
To: Bhushan Bharat-R65777
Cc: kvm-ppc@vger.kernel.org; k...@vger.kernel.org;
ag...@suse.de; Wood
Scott- B07421; Bhushan Bharat-R65777
Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency
only for kernel managed pages
On 07/18/2013 02:04 PM, Bharat Bhushan wrote:
If there is a struct page for the requested mapping then
it's normal DDR and the mapping sets M bit (coherent,
cacheable) else this is treated as I/O and we set I +
G (cache inhibited,
guarded)
This helps setting proper TLB mapping for direct assigned
device
Signed-off-by: Bharat Bhushan
bharat.bhus...@freescale.com
---
arch/powerpc/kvm/e500_mmu_host.c | 17 -
1 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kvm/e500_mmu_host.c
b/arch/powerpc/kvm/e500_mmu_host.c
index 1c6a9d7..089c227 100644
--- a/arch/powerpc/kvm/e500_mmu_host.c
+++ b/arch/powerpc/kvm/e500_mmu_host.c
@@ -64,13 +64,20 @@ static inline u32
e500_shadow_mas3_attrib(u32 mas3, int
usermode)
return mas3;
}
-static inline u32 e500_shadow_mas2_attrib(u32 mas2, int
usermode)
+static inline u32 e500_shadow_mas2_attrib(u32 mas2,
+pfn_t pfn)
{
+ u32 mas2_attr;
+
+ mas2_attr = mas2 MAS2_ATTRIB_MASK;
+
+ if (!pfn_valid(pfn)) {
Why not directly use kvm_is_mmio_pfn()?
What I understand from this function (someone can correct
me) is that it
returns false when the page is managed by kernel and is
not marked as RESERVED (for some reason). For us it does not
matter whether the page is reserved or not, if it is kernel
visible page then it
is DDR.
I think you are setting I|G by addressing all mmio pages,
right? If so,
KVM: direct mmio pfn check
Userspace may specify memory slots that are backed by
mmio pages rather than
normal RAM. In some cases it is not enough to identify
these mmio
pages
by pfn_valid(). This patch adds checking the PageReserved as
well.
Do you know what are those some cases and how checking
PageReserved helps in
those cases?
No, myself didn't see these actual cases in qemu,too. But this
should be chronically persistent as I understand ;-)
Then I will wait till someone educate me :)
The reason is , kvm_is_mmio_pfn() function looks pretty heavy and I do
not want to call this for all tlbwe operation unless it is necessary.
It certainly does more than we need and potentially slows down the fast
path (RAM mapping). The only thing it does on top of if (pfn_valid()) is to
check for pages that are declared reserved on the host. This happens in 2
cases:
1) Non cache coherent DMA
2) Memory hot remove
The non coherent DMA case would be interesting, as with the mechanism
as
it is in place in Linux today, we could potentially break normal guest
operation
if we don't take it into account. However, it's Kconfig guarded by:
depends on 4xx || 8xx || E200 || PPC_MPC512x || GAMECUBE_COMMON
Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On 24.07.2013, at 11:35, Gleb Natapov wrote: On Wed, Jul 24, 2013 at 11:21:11AM +0200, Alexander Graf wrote: Are not we going to use page_is_ram() from e500_shadow_mas2_attrib() as Scott commented? rWhy aren't we using page_is_ram() in kvm_is_mmio_pfn()? Because it is much slower and, IIRC, actually used to build pfn map that allow us to check quickly for valid pfn. Then why should we use page_is_ram()? :) I really don't want the e500 code to diverge too much from what the rest of the kvm code is doing. Alex -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
Copying Andrea for him to verify that I am not talking nonsense :)
On Wed, Jul 24, 2013 at 10:25:20AM +0200, Alexander Graf wrote:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..5e8635b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,6 +102,10 @@ static bool largepages_enabled = true;
bool kvm_is_mmio_pfn(pfn_t pfn)
{
+#ifdef CONFIG_MEMORY_HOTPLUG
I'd feel safer if we narrow this down to e500.
+ /*
+* Currently only in memory hot remove case we may still need this.
+*/
if (pfn_valid(pfn)) {
We still have to check for pfn_valid, no? So the #ifdef should be down here.
int reserved;
struct page *tail = pfn_to_page(pfn);
@@ -124,6 +128,7 @@ bool kvm_is_mmio_pfn(pfn_t pfn)
}
return PageReserved(tail);
}
+#endif
return true;
}
Before apply this change:
real(1m19.954s + 1m20.918s + 1m22.740s + 1m21.146s + 1m22.120s)/5=
1m21.376s
user(0m23.181s + 0m23.550s + 0m23.506s + 0m23.410s + 0m23.520s)/5=
0m23.433s
sys (0m49.087s + 0m49.563s + 0m51.758s + 0m50.290s + 0m51.047s)/5= 0m50.349s
After apply this change:
real(1m19.507s + 1m20.919s + 1m21.436s + 1m21.179s + 1m20.293s)/5=
1m20.667s
user(0m22.595s + 0m22.719s + 0m22.484s + 0m22.811s + 0m22.467s)/5=
0m22.615s
sys (0m48.841s + 0m49.929s + 0m50.310s + 0m49.813s + 0m48.587s)/5= 0m49.496s
So,
real(1m20.667s - 1m21.376s)/1m21.376s x 100% = -0.6%
user(0m22.615s - 0m23.433s)/0m23.433s x 100% = -3.5%
sys (0m49.496s - 0m50.349s)/0m50.349s x 100% = -1.7%
Very nice, so there is a real world performance benefit to doing this. Then
yes, I think it would make sense to change the global helper function to be
fast on e500 and use that one from e500_shadow_mas2_attrib() instead.
Gleb, Paolo, any hard feelings?
I do not see how can we break the function in such a way and get
away with it. Not all valid pfns point to memory. Physical address can
be sparse (due to PCI hole, framebuffer or just because).
--
Gleb.
--
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the body of a message to majord...@vger.kernel.org
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Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On 24.07.2013, at 12:01, Gleb Natapov wrote:
Copying Andrea for him to verify that I am not talking nonsense :)
On Wed, Jul 24, 2013 at 10:25:20AM +0200, Alexander Graf wrote:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..5e8635b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,6 +102,10 @@ static bool largepages_enabled = true;
bool kvm_is_mmio_pfn(pfn_t pfn)
{
+#ifdef CONFIG_MEMORY_HOTPLUG
I'd feel safer if we narrow this down to e500.
+ /*
+* Currently only in memory hot remove case we may still need this.
+*/
if (pfn_valid(pfn)) {
We still have to check for pfn_valid, no? So the #ifdef should be down here.
int reserved;
struct page *tail = pfn_to_page(pfn);
@@ -124,6 +128,7 @@ bool kvm_is_mmio_pfn(pfn_t pfn)
}
return PageReserved(tail);
}
+#endif
return true;
}
Before apply this change:
real(1m19.954s + 1m20.918s + 1m22.740s + 1m21.146s + 1m22.120s)/5=
1m21.376s
user(0m23.181s + 0m23.550s + 0m23.506s + 0m23.410s + 0m23.520s)/5=
0m23.433s
sys (0m49.087s + 0m49.563s + 0m51.758s + 0m50.290s + 0m51.047s)/5= 0m50.349s
After apply this change:
real(1m19.507s + 1m20.919s + 1m21.436s + 1m21.179s + 1m20.293s)/5=
1m20.667s
user(0m22.595s + 0m22.719s + 0m22.484s + 0m22.811s + 0m22.467s)/5=
0m22.615s
sys (0m48.841s + 0m49.929s + 0m50.310s + 0m49.813s + 0m48.587s)/5= 0m49.496s
So,
real(1m20.667s - 1m21.376s)/1m21.376s x 100% = -0.6%
user(0m22.615s - 0m23.433s)/0m23.433s x 100% = -3.5%
sys (0m49.496s - 0m50.349s)/0m50.349s x 100% = -1.7%
Very nice, so there is a real world performance benefit to doing this. Then
yes, I think it would make sense to change the global helper function to be
fast on e500 and use that one from e500_shadow_mas2_attrib() instead.
Gleb, Paolo, any hard feelings?
I do not see how can we break the function in such a way and get
away with it. Not all valid pfns point to memory. Physical address can
be sparse (due to PCI hole, framebuffer or just because).
But we don't check for sparseness today in here either. We merely check for
incomplete huge pages.
Alex
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On Wed, Jul 24, 2013 at 12:09:42PM +0200, Alexander Graf wrote:
On 24.07.2013, at 12:01, Gleb Natapov wrote:
Copying Andrea for him to verify that I am not talking nonsense :)
On Wed, Jul 24, 2013 at 10:25:20AM +0200, Alexander Graf wrote:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..5e8635b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,6 +102,10 @@ static bool largepages_enabled = true;
bool kvm_is_mmio_pfn(pfn_t pfn)
{
+#ifdef CONFIG_MEMORY_HOTPLUG
I'd feel safer if we narrow this down to e500.
+ /*
+* Currently only in memory hot remove case we may still need
this.
+*/
if (pfn_valid(pfn)) {
We still have to check for pfn_valid, no? So the #ifdef should be down
here.
int reserved;
struct page *tail = pfn_to_page(pfn);
@@ -124,6 +128,7 @@ bool kvm_is_mmio_pfn(pfn_t pfn)
}
return PageReserved(tail);
}
+#endif
return true;
}
Before apply this change:
real(1m19.954s + 1m20.918s + 1m22.740s + 1m21.146s + 1m22.120s)/5=
1m21.376s
user(0m23.181s + 0m23.550s + 0m23.506s + 0m23.410s + 0m23.520s)/5=
0m23.433s
sys (0m49.087s + 0m49.563s + 0m51.758s + 0m50.290s + 0m51.047s)/5=
0m50.349s
After apply this change:
real(1m19.507s + 1m20.919s + 1m21.436s + 1m21.179s + 1m20.293s)/5=
1m20.667s
user(0m22.595s + 0m22.719s + 0m22.484s + 0m22.811s + 0m22.467s)/5=
0m22.615s
sys (0m48.841s + 0m49.929s + 0m50.310s + 0m49.813s + 0m48.587s)/5=
0m49.496s
So,
real(1m20.667s - 1m21.376s)/1m21.376s x 100% = -0.6%
user(0m22.615s - 0m23.433s)/0m23.433s x 100% = -3.5%
sys (0m49.496s - 0m50.349s)/0m50.349s x 100% = -1.7%
Very nice, so there is a real world performance benefit to doing this.
Then yes, I think it would make sense to change the global helper function
to be fast on e500 and use that one from e500_shadow_mas2_attrib() instead.
Gleb, Paolo, any hard feelings?
I do not see how can we break the function in such a way and get
away with it. Not all valid pfns point to memory. Physical address can
be sparse (due to PCI hole, framebuffer or just because).
But we don't check for sparseness today in here either. We merely check for
incomplete huge pages.
That's not how I read the code. The code checks for reserved flag set.
It should be set on pfns that point to memory holes. As far as I
understand huge page tricks they are there to guaranty that THP does not
change flags under us, Andrea?
--
Gleb.
--
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the body of a message to majord...@vger.kernel.org
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Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On 24.07.2013, at 12:19, Gleb Natapov wrote:
On Wed, Jul 24, 2013 at 12:09:42PM +0200, Alexander Graf wrote:
On 24.07.2013, at 12:01, Gleb Natapov wrote:
Copying Andrea for him to verify that I am not talking nonsense :)
On Wed, Jul 24, 2013 at 10:25:20AM +0200, Alexander Graf wrote:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..5e8635b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,6 +102,10 @@ static bool largepages_enabled = true;
bool kvm_is_mmio_pfn(pfn_t pfn)
{
+#ifdef CONFIG_MEMORY_HOTPLUG
I'd feel safer if we narrow this down to e500.
+ /*
+* Currently only in memory hot remove case we may still need
this.
+*/
if (pfn_valid(pfn)) {
We still have to check for pfn_valid, no? So the #ifdef should be down
here.
int reserved;
struct page *tail = pfn_to_page(pfn);
@@ -124,6 +128,7 @@ bool kvm_is_mmio_pfn(pfn_t pfn)
}
return PageReserved(tail);
}
+#endif
return true;
}
Before apply this change:
real(1m19.954s + 1m20.918s + 1m22.740s + 1m21.146s + 1m22.120s)/5=
1m21.376s
user(0m23.181s + 0m23.550s + 0m23.506s + 0m23.410s + 0m23.520s)/5=
0m23.433s
sys (0m49.087s + 0m49.563s + 0m51.758s + 0m50.290s + 0m51.047s)/5=
0m50.349s
After apply this change:
real(1m19.507s + 1m20.919s + 1m21.436s + 1m21.179s + 1m20.293s)/5=
1m20.667s
user(0m22.595s + 0m22.719s + 0m22.484s + 0m22.811s + 0m22.467s)/5=
0m22.615s
sys (0m48.841s + 0m49.929s + 0m50.310s + 0m49.813s + 0m48.587s)/5=
0m49.496s
So,
real(1m20.667s - 1m21.376s)/1m21.376s x 100% = -0.6%
user(0m22.615s - 0m23.433s)/0m23.433s x 100% = -3.5%
sys (0m49.496s - 0m50.349s)/0m50.349s x 100% = -1.7%
Very nice, so there is a real world performance benefit to doing this.
Then yes, I think it would make sense to change the global helper function
to be fast on e500 and use that one from e500_shadow_mas2_attrib() instead.
Gleb, Paolo, any hard feelings?
I do not see how can we break the function in such a way and get
away with it. Not all valid pfns point to memory. Physical address can
be sparse (due to PCI hole, framebuffer or just because).
But we don't check for sparseness today in here either. We merely check for
incomplete huge pages.
That's not how I read the code. The code checks for reserved flag set.
It should be set on pfns that point to memory holes. As far as I
I couldn't find any traces of code that sets the reserved bits on e500 chips
though. I've only seen it getting set for memory hotplug and memory incoherent
DMA code which doesn't get used on e500.
But I'd be more than happy to get proven wrong :).
Alex
understand huge page tricks they are there to guaranty that THP does not
change flags under us, Andrea?
--
Gleb.
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Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On Wed, Jul 24, 2013 at 12:25:18PM +0200, Alexander Graf wrote:
On 24.07.2013, at 12:19, Gleb Natapov wrote:
On Wed, Jul 24, 2013 at 12:09:42PM +0200, Alexander Graf wrote:
On 24.07.2013, at 12:01, Gleb Natapov wrote:
Copying Andrea for him to verify that I am not talking nonsense :)
On Wed, Jul 24, 2013 at 10:25:20AM +0200, Alexander Graf wrote:
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1580dd4..5e8635b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,6 +102,10 @@ static bool largepages_enabled = true;
bool kvm_is_mmio_pfn(pfn_t pfn)
{
+#ifdef CONFIG_MEMORY_HOTPLUG
I'd feel safer if we narrow this down to e500.
+ /*
+* Currently only in memory hot remove case we may still need
this.
+*/
if (pfn_valid(pfn)) {
We still have to check for pfn_valid, no? So the #ifdef should be down
here.
int reserved;
struct page *tail = pfn_to_page(pfn);
@@ -124,6 +128,7 @@ bool kvm_is_mmio_pfn(pfn_t pfn)
}
return PageReserved(tail);
}
+#endif
return true;
}
Before apply this change:
real(1m19.954s + 1m20.918s + 1m22.740s + 1m21.146s + 1m22.120s)/5=
1m21.376s
user(0m23.181s + 0m23.550s + 0m23.506s + 0m23.410s + 0m23.520s)/5=
0m23.433s
sys (0m49.087s + 0m49.563s + 0m51.758s + 0m50.290s + 0m51.047s)/5=
0m50.349s
After apply this change:
real(1m19.507s + 1m20.919s + 1m21.436s + 1m21.179s + 1m20.293s)/5=
1m20.667s
user(0m22.595s + 0m22.719s + 0m22.484s + 0m22.811s + 0m22.467s)/5=
0m22.615s
sys (0m48.841s + 0m49.929s + 0m50.310s + 0m49.813s + 0m48.587s)/5=
0m49.496s
So,
real(1m20.667s - 1m21.376s)/1m21.376s x 100% = -0.6%
user(0m22.615s - 0m23.433s)/0m23.433s x 100% = -3.5%
sys (0m49.496s - 0m50.349s)/0m50.349s x 100% = -1.7%
Very nice, so there is a real world performance benefit to doing this.
Then yes, I think it would make sense to change the global helper
function to be fast on e500 and use that one from
e500_shadow_mas2_attrib() instead.
Gleb, Paolo, any hard feelings?
I do not see how can we break the function in such a way and get
away with it. Not all valid pfns point to memory. Physical address can
be sparse (due to PCI hole, framebuffer or just because).
But we don't check for sparseness today in here either. We merely check
for incomplete huge pages.
That's not how I read the code. The code checks for reserved flag set.
It should be set on pfns that point to memory holes. As far as I
I couldn't find any traces of code that sets the reserved bits on e500 chips
though. I've only seen it getting set for memory hotplug and memory
incoherent DMA code which doesn't get used on e500.
But I'd be more than happy to get proven wrong :).
Can you write a module that scans all page structures? AFAIK all pages
are marked as reserved and then those that become regular memory are
marked as unreserved. Hope Andrea will chime in here :)
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Gleb.
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Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages
On 07/24/2013 04:39:59 AM, Alexander Graf wrote: On 24.07.2013, at 11:35, Gleb Natapov wrote: On Wed, Jul 24, 2013 at 11:21:11AM +0200, Alexander Graf wrote: Are not we going to use page_is_ram() from e500_shadow_mas2_attrib() as Scott commented? rWhy aren't we using page_is_ram() in kvm_is_mmio_pfn()? Because it is much slower and, IIRC, actually used to build pfn map that allow us to check quickly for valid pfn. Then why should we use page_is_ram()? :) I really don't want the e500 code to diverge too much from what the rest of the kvm code is doing. I don't understand actually used to build pfn map What code is this? I don't see any calls to page_is_ram() in the KVM code, or in generic mm code. Is this a statement about what x86 does? On PPC page_is_ram() is only called (AFAICT) for determining what attributes to set on mmaps. We want to be sure that KVM always makes the same decision. While pfn_valid() seems like it should be equivalent, it's not obvious from the PPC code that it is. If pfn_valid() is better, why is that not used for mmap? Why are there two different names for the same thing? -Scott -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 04/10] powerpc: Prepare to support kernel handling of IOMMU map/unmap
On Tue, 23 Jul 2013 12:22:59 +1000 Alexey Kardashevskiy a...@ozlabs.ru wrote: Ping, anyone, please? ew, you top-posted. Ben needs ack from any of MM people before proceeding with this patch. Thanks! For what? The three lines of comment in page-flags.h? ack :) Manipulating page-_count directly is considered poor form. Don't blame us if we break your code ;) Actually, the manipulation in realmode_get_page() duplicates the existing get_page_unless_zero() and the one in realmode_put_page() could perhaps be placed in mm.h with a suitable name and some documentation. That would improve your form and might protect the code from getting broken later on. -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 04/10] powerpc: Prepare to support kernel handling of IOMMU map/unmap
On Wed, 2013-07-24 at 15:43 -0700, Andrew Morton wrote: For what? The three lines of comment in page-flags.h? ack :) Manipulating page-_count directly is considered poor form. Don't blame us if we break your code ;) Actually, the manipulation in realmode_get_page() duplicates the existing get_page_unless_zero() and the one in realmode_put_page() could perhaps be placed in mm.h with a suitable name and some documentation. That would improve your form and might protect the code from getting broken later on. Yes, this stuff makes me really nervous :-) If it didn't provide an order of magnitude performance improvement in KVM I would avoid it but heh... Alexey, I like having that stuff in generic code. However the meaning of the words real mode can be ambiguous accross architectures, it might be best to then name it mmu_off_put_page to make things a bit clearer, along with a comment explaining that this is called in a context where none of the virtual mappings are accessible (vmalloc, vmemmap, IOs, ...), and that in the case of sparsemem vmemmap the caller must have taken care of getting the physical address of the struct page and of ensuring it isn't split accross two vmemmap blocks. Cheers, Ben. -- To unsubscribe from this list: send the line unsubscribe kvm-ppc in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
