* [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
@ 2024-11-20 15:06 Uros Bizjak
2024-11-20 15:34 ` Alex Elder
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Uros Bizjak @ 2024-11-20 15:06 UTC (permalink / raw)
To: linux-xfs, linux-kernel
Cc: Uros Bizjak, Chandan Babu R, Darrick J. Wong, Christoph Hellwig,
Dave Chinner
try_cmpxchg() loop with constant "new" value can be substituted
with just xchg() to atomically get and clear the location.
The code on x86_64 improves from:
1e7f: 48 89 4c 24 10 mov %rcx,0x10(%rsp)
1e84: 48 03 14 c5 00 00 00 add 0x0(,%rax,8),%rdx
1e8b: 00
1e88: R_X86_64_32S __per_cpu_offset
1e8c: 8b 02 mov (%rdx),%eax
1e8e: 41 89 c5 mov %eax,%r13d
1e91: 31 c9 xor %ecx,%ecx
1e93: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
1e97: 75 f5 jne 1e8e <xlog_cil_commit+0x84e>
1e99: 48 8b 4c 24 10 mov 0x10(%rsp),%rcx
1e9e: 45 01 e9 add %r13d,%r9d
to just:
1e7f: 48 03 14 cd 00 00 00 add 0x0(,%rcx,8),%rdx
1e86: 00
1e83: R_X86_64_32S __per_cpu_offset
1e87: 31 c9 xor %ecx,%ecx
1e89: 87 0a xchg %ecx,(%rdx)
1e8b: 41 01 cb add %ecx,%r11d
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Chandan Babu R <chandan.babu@oracle.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_log_cil.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 80da0cf87d7a..9d667be1d909 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -171,11 +171,8 @@ xlog_cil_insert_pcp_aggregate(
*/
for_each_cpu(cpu, &ctx->cil_pcpmask) {
struct xlog_cil_pcp *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
- int old = READ_ONCE(cilpcp->space_used);
- while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
- ;
- count += old;
+ count += xchg(&cilpcp->space_used, 0);
}
atomic_add(count, &ctx->space_used);
}
--
2.42.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
2024-11-20 15:06 [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate() Uros Bizjak
@ 2024-11-20 15:34 ` Alex Elder
2024-11-20 15:36 ` Uros Bizjak
2024-11-20 20:37 ` Dave Chinner
2024-11-28 12:19 ` Carlos Maiolino
2 siblings, 1 reply; 6+ messages in thread
From: Alex Elder @ 2024-11-20 15:34 UTC (permalink / raw)
To: Uros Bizjak, linux-xfs, linux-kernel
Cc: Chandan Babu R, Darrick J. Wong, Christoph Hellwig, Dave Chinner
On 11/20/24 9:06 AM, Uros Bizjak wrote:
> try_cmpxchg() loop with constant "new" value can be substituted
> with just xchg() to atomically get and clear the location.
You're right. With a constant new value (0), there is no need
to loop to ensure we get a "stable" update.
Is the READ_ONCE() is still needed?
-Alex
> The code on x86_64 improves from:
>
> 1e7f: 48 89 4c 24 10 mov %rcx,0x10(%rsp)
> 1e84: 48 03 14 c5 00 00 00 add 0x0(,%rax,8),%rdx
> 1e8b: 00
> 1e88: R_X86_64_32S __per_cpu_offset
> 1e8c: 8b 02 mov (%rdx),%eax
> 1e8e: 41 89 c5 mov %eax,%r13d
> 1e91: 31 c9 xor %ecx,%ecx
> 1e93: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
> 1e97: 75 f5 jne 1e8e <xlog_cil_commit+0x84e>
> 1e99: 48 8b 4c 24 10 mov 0x10(%rsp),%rcx
> 1e9e: 45 01 e9 add %r13d,%r9d
>
> to just:
>
> 1e7f: 48 03 14 cd 00 00 00 add 0x0(,%rcx,8),%rdx
> 1e86: 00
> 1e83: R_X86_64_32S __per_cpu_offset
> 1e87: 31 c9 xor %ecx,%ecx
> 1e89: 87 0a xchg %ecx,(%rdx)
> 1e8b: 41 01 cb add %ecx,%r11d
>
> No functional change intended.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Chandan Babu R <chandan.babu@oracle.com>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log_cil.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 80da0cf87d7a..9d667be1d909 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -171,11 +171,8 @@ xlog_cil_insert_pcp_aggregate(
> */
> for_each_cpu(cpu, &ctx->cil_pcpmask) {
> struct xlog_cil_pcp *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
> - int old = READ_ONCE(cilpcp->space_used);
>
> - while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
> - ;
> - count += old;
> + count += xchg(&cilpcp->space_used, 0);
> }
> atomic_add(count, &ctx->space_used);
> }
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
2024-11-20 15:34 ` Alex Elder
@ 2024-11-20 15:36 ` Uros Bizjak
2024-11-20 15:37 ` Alex Elder
0 siblings, 1 reply; 6+ messages in thread
From: Uros Bizjak @ 2024-11-20 15:36 UTC (permalink / raw)
To: Alex Elder
Cc: linux-xfs, linux-kernel, Chandan Babu R, Darrick J. Wong,
Christoph Hellwig, Dave Chinner
On Wed, Nov 20, 2024 at 4:34 PM Alex Elder <elder@riscstar.com> wrote:
>
> On 11/20/24 9:06 AM, Uros Bizjak wrote:
> > try_cmpxchg() loop with constant "new" value can be substituted
> > with just xchg() to atomically get and clear the location.
>
> You're right. With a constant new value (0), there is no need
> to loop to ensure we get a "stable" update.
>
> Is the READ_ONCE() is still needed?
No, xchg() guarantees atomic access on its own.
Uros.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
2024-11-20 15:36 ` Uros Bizjak
@ 2024-11-20 15:37 ` Alex Elder
0 siblings, 0 replies; 6+ messages in thread
From: Alex Elder @ 2024-11-20 15:37 UTC (permalink / raw)
To: Uros Bizjak
Cc: linux-xfs, linux-kernel, Chandan Babu R, Darrick J. Wong,
Christoph Hellwig, Dave Chinner
On 11/20/24 9:36 AM, Uros Bizjak wrote:
> On Wed, Nov 20, 2024 at 4:34 PM Alex Elder <elder@riscstar.com> wrote:
>>
>> On 11/20/24 9:06 AM, Uros Bizjak wrote:
>>> try_cmpxchg() loop with constant "new" value can be substituted
>>> with just xchg() to atomically get and clear the location.
>>
>> You're right. With a constant new value (0), there is no need
>> to loop to ensure we get a "stable" update.
>>
>> Is the READ_ONCE() is still needed?
>
> No, xchg() guarantees atomic access on its own.
>
> Uros.
Based on that:
Reviewed-by: Alex Elder <elder@riscstar.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
2024-11-20 15:06 [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate() Uros Bizjak
2024-11-20 15:34 ` Alex Elder
@ 2024-11-20 20:37 ` Dave Chinner
2024-11-28 12:19 ` Carlos Maiolino
2 siblings, 0 replies; 6+ messages in thread
From: Dave Chinner @ 2024-11-20 20:37 UTC (permalink / raw)
To: Uros Bizjak
Cc: linux-xfs, linux-kernel, Chandan Babu R, Darrick J. Wong,
Christoph Hellwig, Dave Chinner
On Wed, Nov 20, 2024 at 04:06:22PM +0100, Uros Bizjak wrote:
> try_cmpxchg() loop with constant "new" value can be substituted
> with just xchg() to atomically get and clear the location.
>
> The code on x86_64 improves from:
>
> 1e7f: 48 89 4c 24 10 mov %rcx,0x10(%rsp)
> 1e84: 48 03 14 c5 00 00 00 add 0x0(,%rax,8),%rdx
> 1e8b: 00
> 1e88: R_X86_64_32S __per_cpu_offset
> 1e8c: 8b 02 mov (%rdx),%eax
> 1e8e: 41 89 c5 mov %eax,%r13d
> 1e91: 31 c9 xor %ecx,%ecx
> 1e93: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
> 1e97: 75 f5 jne 1e8e <xlog_cil_commit+0x84e>
> 1e99: 48 8b 4c 24 10 mov 0x10(%rsp),%rcx
> 1e9e: 45 01 e9 add %r13d,%r9d
>
> to just:
>
> 1e7f: 48 03 14 cd 00 00 00 add 0x0(,%rcx,8),%rdx
> 1e86: 00
> 1e83: R_X86_64_32S __per_cpu_offset
> 1e87: 31 c9 xor %ecx,%ecx
> 1e89: 87 0a xchg %ecx,(%rdx)
> 1e8b: 41 01 cb add %ecx,%r11d
>
> No functional change intended.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Chandan Babu R <chandan.babu@oracle.com>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log_cil.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 80da0cf87d7a..9d667be1d909 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -171,11 +171,8 @@ xlog_cil_insert_pcp_aggregate(
> */
> for_each_cpu(cpu, &ctx->cil_pcpmask) {
> struct xlog_cil_pcp *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
> - int old = READ_ONCE(cilpcp->space_used);
>
> - while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
> - ;
> - count += old;
> + count += xchg(&cilpcp->space_used, 0);
> }
> atomic_add(count, &ctx->space_used);
> }
Looks fine.
Reviewed-by: Dave Chinner <dchinner@redhat.com>
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
2024-11-20 15:06 [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate() Uros Bizjak
2024-11-20 15:34 ` Alex Elder
2024-11-20 20:37 ` Dave Chinner
@ 2024-11-28 12:19 ` Carlos Maiolino
2 siblings, 0 replies; 6+ messages in thread
From: Carlos Maiolino @ 2024-11-28 12:19 UTC (permalink / raw)
To: linux-xfs, linux-kernel, Uros Bizjak
Cc: Chandan Babu R, Darrick J. Wong, Christoph Hellwig, Dave Chinner
On Wed, 20 Nov 2024 16:06:22 +0100, Uros Bizjak wrote:
> try_cmpxchg() loop with constant "new" value can be substituted
> with just xchg() to atomically get and clear the location.
>
> The code on x86_64 improves from:
>
> 1e7f: 48 89 4c 24 10 mov %rcx,0x10(%rsp)
> 1e84: 48 03 14 c5 00 00 00 add 0x0(,%rax,8),%rdx
> 1e8b: 00
> 1e88: R_X86_64_32S __per_cpu_offset
> 1e8c: 8b 02 mov (%rdx),%eax
> 1e8e: 41 89 c5 mov %eax,%r13d
> 1e91: 31 c9 xor %ecx,%ecx
> 1e93: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
> 1e97: 75 f5 jne 1e8e <xlog_cil_commit+0x84e>
> 1e99: 48 8b 4c 24 10 mov 0x10(%rsp),%rcx
> 1e9e: 45 01 e9 add %r13d,%r9d
>
> [...]
Applied to for-next, thanks!
[1/1] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate()
commit: 214093534f3c046bf5acc9affbf4e6bd9af4538b
Best regards,
--
Carlos Maiolino <cem@kernel.org>
^ permalink raw reply [flat|nested] 6+ messages in thread
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2024-11-20 15:06 [PATCH] xfs: Use xchg() in xlog_cil_insert_pcp_aggregate() Uros Bizjak
2024-11-20 15:34 ` Alex Elder
2024-11-20 15:36 ` Uros Bizjak
2024-11-20 15:37 ` Alex Elder
2024-11-20 20:37 ` Dave Chinner
2024-11-28 12:19 ` Carlos Maiolino
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