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Commit 6ee4752f authored by David Chinner's avatar David Chinner Committed by Lachlan McIlroy
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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: default avatarDavid Chinner <dgc@sgi.com>
Signed-off-by: default avatarChristoph Hellwig <hch@infradead.org>
Signed-off-by: default avatarLachlan McIlroy <lachlan@sgi.com>
parent 44d814ce

fs/xfs/support/ktrace.c

+8 −13
Original line number Diff line number Diff line
@@ -92,7 +92,7 @@ ktrace_alloc(int nentries, unsigned int __nocast sleep) 


	ktp->kt_entries  = ktep;

	ktp->kt_nentries = nentries;

	ktp->kt_index    = 0;

	atomic_set(&ktp->kt_index, 0);

	ktp->kt_rollover = 0;

	return ktp;

}
@@ -151,8 +151,6 @@ ktrace_enter( 
	void            *val14,

	void            *val15)

{

	static DEFINE_SPINLOCK(wrap_lock);

	unsigned long	flags;

	int             index;

	ktrace_entry_t  *ktep;
@@ -161,12 +159,8 @@ ktrace_enter( 
	/*

	 * Grab an entry by pushing the index up to the next one.

	 */

	spin_lock_irqsave(&wrap_lock, flags);

	index = ktp->kt_index;

	if (++ktp->kt_index == ktp->kt_nentries)

		ktp->kt_index = 0;

	spin_unlock_irqrestore(&wrap_lock, flags);



	index = atomic_add_return(1, &ktp->kt_index);

	index = (index - 1) % ktp->kt_nentries;

	if (!ktp->kt_rollover && index == ktp->kt_nentries - 1)

		ktp->kt_rollover = 1;
@@ -199,11 +193,12 @@ int 
ktrace_nentries(

	ktrace_t        *ktp)

{

	if (ktp == NULL) {

	int	index;

	if (ktp == NULL)

		return 0;

	}



	return (ktp->kt_rollover ? ktp->kt_nentries : ktp->kt_index);

	index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;

	return (ktp->kt_rollover ? ktp->kt_nentries : index);

}



/*
@@ -228,7 +223,7 @@ ktrace_first(ktrace_t *ktp, ktrace_snap_t *ktsp) 
	int             nentries;



	if (ktp->kt_rollover)

		index = ktp->kt_index;

		index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;

	else

		index = 0;

fs/xfs/support/ktrace.h

+1 −1
Original line number Diff line number Diff line
@@ -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;