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linux-sg2042
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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: Mathias Krause <mathias.krause@secunet.com>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Mathias Krause 2013-10-25 12:14:15 +02:00 committed by Herbert Xu
parent cfc6f11b76
commit 0b6b098efc
2 changed files with 5 additions and 7 deletions
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3
include/linux/padata.h
View File

@ -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;
};

9
kernel/padata.c
View File

@ -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;