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xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()

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Use !try_cmpxchg instead of cmpxchg (*ptr, old, new) != old in
xlog_cil_insert_pcp_aggregate().  x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg.

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails. There is no need to re-read the value in the loop.

Note that the value from *ptr should be read using READ_ONCE to
prevent the compiler from merging, refetching or reordering the read.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Cc: Chandan Babu R <chandan.babu@oracle.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Uros Bizjak 2024-09-23 14:22:17 +02:00 committed by Carlos Maiolino
parent 6148b77960
commit 20195d011c
1 changed files with 4 additions and 7 deletions
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11
fs/xfs/xfs_log_cil.c
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@ -156,7 +156,6 @@ xlog_cil_insert_pcp_aggregate(
struct xfs_cil *cil,
struct xfs_cil_ctx *ctx)
{
struct xlog_cil_pcp *cilpcp;
int cpu;
int count = 0;
@ -171,13 +170,11 @@ xlog_cil_insert_pcp_aggregate(
* structures that could have a nonzero space_used.
*/
for_each_cpu(cpu, &ctx->cil_pcpmask) {
int old, prev;
struct xlog_cil_pcp *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
int old = READ_ONCE(cilpcp->space_used);
cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
do {
old = cilpcp->space_used;
prev = cmpxchg(&cilpcp->space_used, old, 0);
} while (old != prev);
while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
;
count += old;
}
atomic_add(count, &ctx->space_used);