| Message ID | 20240922170746.11361-1-ubizjak@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [v2] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate() | expand |
> { > - struct xlog_cil_pcp *cilpcp; > - int cpu; > - int count = 0; > + int cpu; > + int count = 0; This should not be reformatted, but maye Carlos can fix it up when applying the patch. Otherwise looks good: Reviewed-by: Christoph Hellwig <hch@lst.de>
On Mon, Sep 23, 2024 at 2:03 PM Christoph Hellwig <hch@infradead.org> wrote: > > > { > > - struct xlog_cil_pcp *cilpcp; > > - int cpu; > > - int count = 0; > > + int cpu; > > + int count = 0; > > This should not be reformatted, but maye Carlos can fix it up when > applying the patch. Otherwise looks good: I'll just send a v3 with your R-b tag. Thanks, Uros.
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c index 391a938d690c..d4e06e6f050f 100644 --- a/fs/xfs/xfs_log_cil.c +++ b/fs/xfs/xfs_log_cil.c @@ -156,9 +156,8 @@ xlog_cil_insert_pcp_aggregate( struct xfs_cil *cil, struct xfs_cil_ctx *ctx) { - struct xlog_cil_pcp *cilpcp; - int cpu; - int count = 0; + int cpu; + int count = 0; /* Trigger atomic updates then aggregate only for the first caller */ if (!test_and_clear_bit(XLOG_CIL_PCP_SPACE, &cil->xc_flags)) @@ -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);
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> Cc: Chandan Babu R <chandan.babu@oracle.com> Cc: "Darrick J. Wong" <djwong@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> --- v2: Move cilpcp variable into the loop scope. Initialize cilcpc and old variables at the declaration time. Use alternative form of the while loop. --- fs/xfs/xfs_log_cil.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)