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[XFS] Use atomic counters for ktrace buffer indexes

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ktrace_enter() is consuming vast amounts of CPU time due to the use of a
single global lock for protecting buffer index increments. Change it to
use per-buffer atomic counters - this reduces ktrace_enter() overhead
during a trace intensive test on a 4p machine from 58% of all CPU time to
12% and halves test runtime.

SGI-PV: 977546
SGI-Modid: xfs-linux-melb:xfs-kern:30537a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
This commit is contained in:
David Chinner
2008-03-06 13:45:35 +11:00
committed by Lachlan McIlroy
parent 44d814ced4
commit 6ee4752ffe
2 changed files with 9 additions and 14 deletions
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2
fs/xfs/support/ktrace.h
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@@ -30,7 +30,7 @@ typedef struct ktrace_entry {
*/
typedef struct ktrace {
int kt_nentries; /* number of entries in trace buf */
int kt_index; /* current index in entries */
atomic_t kt_index; /* current index in entries */
int kt_rollover;
ktrace_entry_t *kt_entries; /* buffer of entries */
} ktrace_t;