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Commit 0b6b098e authored by Mathias Krause's avatar Mathias Krause Committed by Herbert Xu
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padata: make the sequence counter an atomic_t 



Using a spinlock to atomically increase a counter sounds wrong -- we've
atomic_t for this!

Also move 'seq_nr' to a different cache line than 'lock' to reduce cache
line trashing. This has the nice side effect of decreasing the size of
struct parallel_data from 192 to 128 bytes for a x86-64 build, e.g.
occupying only two instead of three cache lines.

Those changes results in a 5% performance increase on an IPsec test run
using pcrypt.

Btw. the seq_lock spinlock was never explicitly initialized -- one more
reason to get rid of it.

Signed-off-by: default avatarMathias Krause <mathias.krause@secunet.com>
Acked-by: default avatarSteffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent cfc6f11b

include/linux/padata.h

+1 −2
Original line number Diff line number Diff line
@@ -129,10 +129,9 @@ struct parallel_data { 
	struct padata_serial_queue	__percpu *squeue;

	atomic_t			reorder_objects;

	atomic_t			refcnt;

	atomic_t			seq_nr;

	struct padata_cpumask		cpumask;

	spinlock_t                      lock ____cacheline_aligned;

	spinlock_t                      seq_lock;

	unsigned int			seq_nr;

	unsigned int			processed;

	struct timer_list		timer;

};

kernel/padata.c

+4 −5
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index) 


static int padata_cpu_hash(struct parallel_data *pd)

{

	unsigned int seq_nr;

	int cpu_index;



	/*
@@ -53,10 +54,8 @@ static int padata_cpu_hash(struct parallel_data *pd) 
	 * seq_nr mod. number of cpus in use.

	 */



	spin_lock(&pd->seq_lock);

	cpu_index =  pd->seq_nr % cpumask_weight(pd->cpumask.pcpu);

	pd->seq_nr++;

	spin_unlock(&pd->seq_lock);

	seq_nr = atomic_inc_return(&pd->seq_nr);

	cpu_index = seq_nr % cpumask_weight(pd->cpumask.pcpu);



	return padata_index_to_cpu(pd, cpu_index);

}
@@ -429,7 +428,7 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst, 
	padata_init_pqueues(pd);

	padata_init_squeues(pd);

	setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd);

	pd->seq_nr = 0;

	atomic_set(&pd->seq_nr, -1);

	atomic_set(&pd->reorder_objects, 0);

	atomic_set(&pd->refcnt, 0);

	pd->pinst = pinst;