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[XFS] Use atomic counters for ktrace buffer indexes
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>
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parent
44d814ced4
commit
6ee4752ffe
2 changed files with 9 additions and 14 deletions
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@ -92,7 +92,7 @@ ktrace_alloc(int nentries, unsigned int __nocast sleep)
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ktp->kt_entries = ktep;
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ktp->kt_nentries = nentries;
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ktp->kt_index = 0;
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atomic_set(&ktp->kt_index, 0);
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ktp->kt_rollover = 0;
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return ktp;
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}
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@ -151,8 +151,6 @@ ktrace_enter(
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void *val14,
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void *val15)
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{
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static DEFINE_SPINLOCK(wrap_lock);
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unsigned long flags;
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int index;
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ktrace_entry_t *ktep;
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@ -161,12 +159,8 @@ ktrace_enter(
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/*
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* Grab an entry by pushing the index up to the next one.
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*/
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spin_lock_irqsave(&wrap_lock, flags);
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index = ktp->kt_index;
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if (++ktp->kt_index == ktp->kt_nentries)
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ktp->kt_index = 0;
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spin_unlock_irqrestore(&wrap_lock, flags);
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index = atomic_add_return(1, &ktp->kt_index);
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index = (index - 1) % ktp->kt_nentries;
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if (!ktp->kt_rollover && index == ktp->kt_nentries - 1)
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ktp->kt_rollover = 1;
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@ -199,11 +193,12 @@ int
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ktrace_nentries(
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ktrace_t *ktp)
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{
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if (ktp == NULL) {
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int index;
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if (ktp == NULL)
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return 0;
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}
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return (ktp->kt_rollover ? ktp->kt_nentries : ktp->kt_index);
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index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;
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return (ktp->kt_rollover ? ktp->kt_nentries : index);
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}
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/*
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@ -228,7 +223,7 @@ ktrace_first(ktrace_t *ktp, ktrace_snap_t *ktsp)
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int nentries;
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if (ktp->kt_rollover)
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index = ktp->kt_index;
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index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;
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else
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index = 0;
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@ -30,7 +30,7 @@ typedef struct ktrace_entry {
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*/
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typedef struct ktrace {
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int kt_nentries; /* number of entries in trace buf */
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int kt_index; /* current index in entries */
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atomic_t kt_index; /* current index in entries */
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int kt_rollover;
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ktrace_entry_t *kt_entries; /* buffer of entries */
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} ktrace_t;
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