Re: [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Jeff Cody]

On Wed, Feb 22, 2017 at 01:47:10PM +0100, Kevin Wolf wrote:
> Am 17.02.2017 um 22:51 hat Jeff Cody geschrieben:
> > On Fri, Feb 17, 2017 at 03:42:52PM -0600, Eric Blake wrote:
> > > On 02/17/2017 03:37 PM, Jeff Cody wrote:
> > > > On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
> > > >> if the passed qiov contains exactly one iov we can
> > > >> pass the buffer directly.
> > > >>
> > > >> Signed-off-by: Peter Lieven 
> > > >> ---
> > > >>  block/nfs.c | 23 ---
> > > >>  1 file changed, 16 insertions(+), 7 deletions(-)
> > > >>
> > > >> diff --git a/block/nfs.c b/block/nfs.c
> > > >> index ab5dcc2..bb4b75f 100644
> > > >> --- a/block/nfs.c
> > > >> +++ b/block/nfs.c
> > > >> @@ -295,20 +295,27 @@ static int coroutine_fn 
> > > >> nfs_co_pwritev(BlockDriverState *bs, uint64_t offset,
> > > >>  NFSClient *client = bs->opaque;
> > > >>  NFSRPC task;
> > > >>  char *buf = NULL;
> > > >> +bool my_buffer = false;
> > > > 
> > > > g_free() is a nop if buf is NULL, so there is no need for the my_buffer
> > > > variable & check.
> > > 
> > > Umm, yes there is:
> > > 
> > > >> +if (iov->niov != 1) {
> > > >> +buf = g_try_malloc(bytes);
> > > >> +if (bytes && buf == NULL) {
> > > >> +return -ENOMEM;
> > > >> +}
> > > >> +qemu_iovec_to_buf(iov, 0, buf, bytes);
> > > >> +my_buffer = true;
> > > >> +} else {
> > > >> +buf = iov->iov[0].iov_base;
> > > 
> > > If we took the else branch, then we definitely do not want to be calling
> > > g_free(buf).
> > 
> > Doh!
> > 
> > > 
> > > >>  }
> > > >>  
> > > >> -qemu_iovec_to_buf(iov, 0, buf, bytes);
> > > >> -
> > > >>  if (nfs_pwrite_async(client->context, client->fh,
> > > >>   offset, bytes, buf,
> > > >>   nfs_co_generic_cb, ) != 0) {
> > > >> -g_free(buf);
> > > >> +if (my_buffer) {
> > > >> +g_free(buf);
> > > >> +}
> > > 
> > > It looks correct as-is to me.
> > 
> > Indeed.
> > 
> > Reviewed-by: Jeff Cody 
> 
> You gave R-b for both patches, but did not merge it - who is supposed to
> do that?
>

I am going to do it in my next round, I was just waiting to see if there
were any other comments.

Re: [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Kevin Wolf]

Am 17.02.2017 um 22:51 hat Jeff Cody geschrieben:
> On Fri, Feb 17, 2017 at 03:42:52PM -0600, Eric Blake wrote:
> > On 02/17/2017 03:37 PM, Jeff Cody wrote:
> > > On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
> > >> if the passed qiov contains exactly one iov we can
> > >> pass the buffer directly.
> > >>
> > >> Signed-off-by: Peter Lieven 
> > >> ---
> > >>  block/nfs.c | 23 ---
> > >>  1 file changed, 16 insertions(+), 7 deletions(-)
> > >>
> > >> diff --git a/block/nfs.c b/block/nfs.c
> > >> index ab5dcc2..bb4b75f 100644
> > >> --- a/block/nfs.c
> > >> +++ b/block/nfs.c
> > >> @@ -295,20 +295,27 @@ static int coroutine_fn 
> > >> nfs_co_pwritev(BlockDriverState *bs, uint64_t offset,
> > >>  NFSClient *client = bs->opaque;
> > >>  NFSRPC task;
> > >>  char *buf = NULL;
> > >> +bool my_buffer = false;
> > > 
> > > g_free() is a nop if buf is NULL, so there is no need for the my_buffer
> > > variable & check.
> > 
> > Umm, yes there is:
> > 
> > >> +if (iov->niov != 1) {
> > >> +buf = g_try_malloc(bytes);
> > >> +if (bytes && buf == NULL) {
> > >> +return -ENOMEM;
> > >> +}
> > >> +qemu_iovec_to_buf(iov, 0, buf, bytes);
> > >> +my_buffer = true;
> > >> +} else {
> > >> +buf = iov->iov[0].iov_base;
> > 
> > If we took the else branch, then we definitely do not want to be calling
> > g_free(buf).
> 
> Doh!
> 
> > 
> > >>  }
> > >>  
> > >> -qemu_iovec_to_buf(iov, 0, buf, bytes);
> > >> -
> > >>  if (nfs_pwrite_async(client->context, client->fh,
> > >>   offset, bytes, buf,
> > >>   nfs_co_generic_cb, ) != 0) {
> > >> -g_free(buf);
> > >> +if (my_buffer) {
> > >> +g_free(buf);
> > >> +}
> > 
> > It looks correct as-is to me.
> 
> Indeed.
> 
> Reviewed-by: Jeff Cody 

You gave R-b for both patches, but did not merge it - who is supposed to
do that?

Kevin

Re: [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Jeff Cody]

On Fri, Feb 17, 2017 at 03:42:52PM -0600, Eric Blake wrote:
> On 02/17/2017 03:37 PM, Jeff Cody wrote:
> > On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
> >> if the passed qiov contains exactly one iov we can
> >> pass the buffer directly.
> >>
> >> Signed-off-by: Peter Lieven 
> >> ---
> >>  block/nfs.c | 23 ---
> >>  1 file changed, 16 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/block/nfs.c b/block/nfs.c
> >> index ab5dcc2..bb4b75f 100644
> >> --- a/block/nfs.c
> >> +++ b/block/nfs.c
> >> @@ -295,20 +295,27 @@ static int coroutine_fn 
> >> nfs_co_pwritev(BlockDriverState *bs, uint64_t offset,
> >>  NFSClient *client = bs->opaque;
> >>  NFSRPC task;
> >>  char *buf = NULL;
> >> +bool my_buffer = false;
> > 
> > g_free() is a nop if buf is NULL, so there is no need for the my_buffer
> > variable & check.
> 
> Umm, yes there is:
> 
> >> +if (iov->niov != 1) {
> >> +buf = g_try_malloc(bytes);
> >> +if (bytes && buf == NULL) {
> >> +return -ENOMEM;
> >> +}
> >> +qemu_iovec_to_buf(iov, 0, buf, bytes);
> >> +my_buffer = true;
> >> +} else {
> >> +buf = iov->iov[0].iov_base;
> 
> If we took the else branch, then we definitely do not want to be calling
> g_free(buf).

Doh!

> 
> >>  }
> >>  
> >> -qemu_iovec_to_buf(iov, 0, buf, bytes);
> >> -
> >>  if (nfs_pwrite_async(client->context, client->fh,
> >>   offset, bytes, buf,
> >>   nfs_co_generic_cb, ) != 0) {
> >> -g_free(buf);
> >> +if (my_buffer) {
> >> +g_free(buf);
> >> +}
> 
> It looks correct as-is to me.

Indeed.

Reviewed-by: Jeff Cody 

Re: [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Eric Blake]

On 02/17/2017 03:37 PM, Jeff Cody wrote:
> On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
>> if the passed qiov contains exactly one iov we can
>> pass the buffer directly.
>>
>> Signed-off-by: Peter Lieven 
>> ---
>>  block/nfs.c | 23 ---
>>  1 file changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/nfs.c b/block/nfs.c
>> index ab5dcc2..bb4b75f 100644
>> --- a/block/nfs.c
>> +++ b/block/nfs.c
>> @@ -295,20 +295,27 @@ static int coroutine_fn 
>> nfs_co_pwritev(BlockDriverState *bs, uint64_t offset,
>>  NFSClient *client = bs->opaque;
>>  NFSRPC task;
>>  char *buf = NULL;
>> +bool my_buffer = false;
> 
> g_free() is a nop if buf is NULL, so there is no need for the my_buffer
> variable & check.

Umm, yes there is:

>> +if (iov->niov != 1) {
>> +buf = g_try_malloc(bytes);
>> +if (bytes && buf == NULL) {
>> +return -ENOMEM;
>> +}
>> +qemu_iovec_to_buf(iov, 0, buf, bytes);
>> +my_buffer = true;
>> +} else {
>> +buf = iov->iov[0].iov_base;

If we took the else branch, then we definitely do not want to be calling
g_free(buf).

>>  }
>>  
>> -qemu_iovec_to_buf(iov, 0, buf, bytes);
>> -
>>  if (nfs_pwrite_async(client->context, client->fh,
>>   offset, bytes, buf,
>>   nfs_co_generic_cb, ) != 0) {
>> -g_free(buf);
>> +if (my_buffer) {
>> +g_free(buf);
>> +}

It looks correct as-is to me.

-- 
Eric Blake   eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org



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Re: [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Jeff Cody]

On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
> if the passed qiov contains exactly one iov we can
> pass the buffer directly.
> 
> Signed-off-by: Peter Lieven 
> ---
>  block/nfs.c | 23 ---
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/block/nfs.c b/block/nfs.c
> index ab5dcc2..bb4b75f 100644
> --- a/block/nfs.c
> +++ b/block/nfs.c
> @@ -295,20 +295,27 @@ static int coroutine_fn nfs_co_pwritev(BlockDriverState 
> *bs, uint64_t offset,
>  NFSClient *client = bs->opaque;
>  NFSRPC task;
>  char *buf = NULL;
> +bool my_buffer = false;

g_free() is a nop if buf is NULL, so there is no need for the my_buffer
variable & check.

>  
>  nfs_co_init_task(bs, );
>  
> -buf = g_try_malloc(bytes);
> -if (bytes && buf == NULL) {
> -return -ENOMEM;
> +if (iov->niov != 1) {
> +buf = g_try_malloc(bytes);
> +if (bytes && buf == NULL) {
> +return -ENOMEM;
> +}
> +qemu_iovec_to_buf(iov, 0, buf, bytes);
> +my_buffer = true;
> +} else {
> +buf = iov->iov[0].iov_base;
>  }
>  
> -qemu_iovec_to_buf(iov, 0, buf, bytes);
> -
>  if (nfs_pwrite_async(client->context, client->fh,
>   offset, bytes, buf,
>   nfs_co_generic_cb, ) != 0) {
> -g_free(buf);
> +if (my_buffer) {
> +g_free(buf);
> +}
>  return -ENOMEM;
>  }
>  
> @@ -317,7 +324,9 @@ static int coroutine_fn nfs_co_pwritev(BlockDriverState 
> *bs, uint64_t offset,
>  qemu_coroutine_yield();
>  }
>  
> -g_free(buf);
> +if (my_buffer) {
> +g_free(buf);
> +}
>  
>  if (task.ret != bytes) {
>  return task.ret < 0 ? task.ret : -EIO;
> -- 
> 1.9.1
> 

[Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Peter Lieven]

if the passed qiov contains exactly one iov we can
pass the buffer directly.

Signed-off-by: Peter Lieven 
---
 block/nfs.c | 23 ---
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/block/nfs.c b/block/nfs.c
index ab5dcc2..bb4b75f 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -295,20 +295,27 @@ static int coroutine_fn nfs_co_pwritev(BlockDriverState 
*bs, uint64_t offset,
 NFSClient *client = bs->opaque;
 NFSRPC task;
 char *buf = NULL;
+bool my_buffer = false;
 
 nfs_co_init_task(bs, );
 
-buf = g_try_malloc(bytes);
-if (bytes && buf == NULL) {
-return -ENOMEM;
+if (iov->niov != 1) {
+buf = g_try_malloc(bytes);
+if (bytes && buf == NULL) {
+return -ENOMEM;
+}
+qemu_iovec_to_buf(iov, 0, buf, bytes);
+my_buffer = true;
+} else {
+buf = iov->iov[0].iov_base;
 }
 
-qemu_iovec_to_buf(iov, 0, buf, bytes);
-
 if (nfs_pwrite_async(client->context, client->fh,
  offset, bytes, buf,
  nfs_co_generic_cb, ) != 0) {
-g_free(buf);
+if (my_buffer) {
+g_free(buf);
+}
 return -ENOMEM;
 }
 
@@ -317,7 +324,9 @@ static int coroutine_fn nfs_co_pwritev(BlockDriverState 
*bs, uint64_t offset,
 qemu_coroutine_yield();
 }
 
-g_free(buf);
+if (my_buffer) {
+g_free(buf);
+}
 
 if (task.ret != bytes) {
 return task.ret < 0 ? task.ret : -EIO;
-- 
1.9.1