Re: [PATCH V8 01/10] powerpc, perf: Drop the branch sample when 'from' cannot be fetched
On 06/10/2015 08:51 AM, Daniel Axtens wrote: Hi Anshuman, Was there a cover letter for this series that I missed? This is the continuation (rebased and reworked) of the series posted at https://lkml.org/lkml/2014/5/5/153 (which is V6). I remember to have incremented the count for the re-send of the first four patches of the series to Peter Z for generic review which got pulled in last year. These patches here are the remaining powerpc part of the original series. Will list down the current changes as well next time around along with the new ones. On Mon, 2015-06-08 at 17:08 +0530, Anshuman Khandual wrote: BHRB is a rolling buffer. Hence we might end up in a situation where Could you spell out what BHRB stands for? Branch History Rolling Buffer, would you like to have that in the commit message as well ? we have read one target address but when we try to read the next entry indicating the from address of the targe, the buffer just overflows. target? Yeah its target address. In this case, the captured from address will be zero which indicates the end of the buffer. In what sort of situations would this occur? It seems like something we would want to avoid if possible? Its not avoidable. During regular flow of branch recording, the HW would have written both the records correctly but then the new ones came in and we just happen to loose one of them causing this situation. ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH V8 01/10] powerpc, perf: Drop the branch sample when 'from' cannot be fetched
Hi, On Wed, 2015-06-10 at 17:32 +0530, Anshuman Khandual wrote: On 06/10/2015 08:51 AM, Daniel Axtens wrote: Hi Anshuman, Was there a cover letter for this series that I missed? This is the continuation (rebased and reworked) of the series posted at https://lkml.org/lkml/2014/5/5/153 (which is V6). I remember to have incremented the count for the re-send of the first four patches of the series to Peter Z for generic review which got pulled in last year. These patches here are the remaining powerpc part of the original series. Will list down the current changes as well next time around along with the new ones. On Mon, 2015-06-08 at 17:08 +0530, Anshuman Khandual wrote: BHRB is a rolling buffer. Hence we might end up in a situation where Could you spell out what BHRB stands for? Branch History Rolling Buffer, would you like to have that in the commit message as well ? Yes please. we have read one target address but when we try to read the next entry indicating the from address of the targe, the buffer just overflows. target? Yeah its target address. Ok, I was just trying to point out the spelling mistake above. In this case, the captured from address will be zero which indicates the end of the buffer. In what sort of situations would this occur? It seems like something we would want to avoid if possible? Its not avoidable. During regular flow of branch recording, the HW would have written both the records correctly but then the new ones came in and we just happen to loose one of them causing this situation. OK. Regards, Daniel signature.asc Description: This is a digitally signed message part ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH V8 01/10] powerpc, perf: Drop the branch sample when 'from' cannot be fetched
Hi Anshuman,
Was there a cover letter for this series that I missed?
On Mon, 2015-06-08 at 17:08 +0530, Anshuman Khandual wrote:
BHRB is a rolling buffer. Hence we might end up in a situation where
Could you spell out what BHRB stands for?
we have read one target address but when we try to read the next entry
indicating the from address of the targe, the buffer just overflows.
target?
In this case, the captured from address will be zero which indicates
the end of the buffer.
In what sort of situations would this occur? It seems like something we
would want to avoid if possible?
This patch drops the entire branch record which would have otherwise
confused the user space tools.
Signed-off-by: Anshuman Khandual khand...@linux.vnet.ibm.com
---
arch/powerpc/perf/core-book3s.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 12b6384..c246e65 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -452,7 +452,6 @@ static void power_pmu_bhrb_read(struct cpu_hw_events
*cpuhw)
*In this case we need to read the instruction from
*memory to determine the target/to address.
*/
-
if (val BHRB_TARGET) {
/* Target branches use two entries
* (ie. computed gotos/XL form)
@@ -463,6 +462,8 @@ static void power_pmu_bhrb_read(struct cpu_hw_events
*cpuhw)
/* Get from address in next entry */
val = read_bhrb(r_index++);
+ if (!val)
+ break;
addr = val BHRB_EA;
if (val BHRB_TARGET) {
/* Shouldn't have two targets in a
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[PATCH V8 01/10] powerpc, perf: Drop the branch sample when 'from' cannot be fetched
BHRB is a rolling buffer. Hence we might end up in a situation where
we have read one target address but when we try to read the next entry
indicating the from address of the targe, the buffer just overflows.
In this case, the captured from address will be zero which indicates
the end of the buffer.
This patch drops the entire branch record which would have otherwise
confused the user space tools.
Signed-off-by: Anshuman Khandual khand...@linux.vnet.ibm.com
---
arch/powerpc/perf/core-book3s.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 12b6384..c246e65 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -452,7 +452,6 @@ static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
*In this case we need to read the instruction from
*memory to determine the target/to address.
*/
-
if (val BHRB_TARGET) {
/* Target branches use two entries
* (ie. computed gotos/XL form)
@@ -463,6 +462,8 @@ static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
/* Get from address in next entry */
val = read_bhrb(r_index++);
+ if (!val)
+ break;
addr = val BHRB_EA;
if (val BHRB_TARGET) {
/* Shouldn't have two targets in a
--
2.1.0
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