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NFS: Don't run wake_up_bit() when nobody is waiting... 

"perf lock" shows fairly heavy contention for the bit waitqueue locks
when doing an I/O heavy workload.
Use a bit to tell whether or not there has been contention for a lock
so that we can optimise away the bit waitqueue options in those cases.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Trond Myklebust 2017-07-11 17:53:48 -04:00 committed by Anna Schumaker
parent 00422483ad
commit 301bfa4830
2 changed files with 18 additions and 1 deletions
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17
fs/nfs/pagelist.c
View File

@ -155,9 +155,12 @@ nfs_page_group_lock(struct nfs_page *req, bool nonblock)
if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
return 0;
if (!nonblock)
if (!nonblock) {
set_bit(PG_CONTENDED1, &head->wb_flags);
smp_mb__after_atomic();
return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
TASK_UNINTERRUPTIBLE);
}
return -EAGAIN;
}
@ -175,6 +178,10 @@ nfs_page_group_lock_wait(struct nfs_page *req)
WARN_ON_ONCE(head != head->wb_head);
if (!test_bit(PG_HEADLOCK, &head->wb_flags))
return;
set_bit(PG_CONTENDED1, &head->wb_flags);
smp_mb__after_atomic();
wait_on_bit(&head->wb_flags, PG_HEADLOCK,
TASK_UNINTERRUPTIBLE);
}
@ -193,6 +200,8 @@ nfs_page_group_unlock(struct nfs_page *req)
smp_mb__before_atomic();
clear_bit(PG_HEADLOCK, &head->wb_flags);
smp_mb__after_atomic();
if (!test_bit(PG_CONTENDED1, &head->wb_flags))
return;
wake_up_bit(&head->wb_flags, PG_HEADLOCK);
}
@ -383,6 +392,8 @@ void nfs_unlock_request(struct nfs_page *req)
smp_mb__before_atomic();
clear_bit(PG_BUSY, &req->wb_flags);
smp_mb__after_atomic();
if (!test_bit(PG_CONTENDED2, &req->wb_flags))
return;
wake_up_bit(&req->wb_flags, PG_BUSY);
}
@ -465,6 +476,10 @@ void nfs_release_request(struct nfs_page *req)
int
nfs_wait_on_request(struct nfs_page *req)
{
if (!test_bit(PG_BUSY, &req->wb_flags))
return 0;
set_bit(PG_CONTENDED2, &req->wb_flags);
smp_mb__after_atomic();
return wait_on_bit_io(&req->wb_flags, PG_BUSY,
TASK_UNINTERRUPTIBLE);
}

2
include/linux/nfs_page.h
View File

@ -33,6 +33,8 @@ enum {
PG_UPTODATE, /* page group sync bit in read path */
PG_WB_END, /* page group sync bit in write path */
PG_REMOVE, /* page group sync bit in write path */
PG_CONTENDED1, /* Is someone waiting for a lock? */
PG_CONTENDED2, /* Is someone waiting for a lock? */
};
struct nfs_inode;