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author | NeilBrown <neilb@suse.de> | 2010-08-12 17:04:06 +1000 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2010-09-07 19:22:07 -0400 |
commit | f16b6e8d838b2e2bb4561201311c66ac02ad67df (patch) | |
tree | 92c4ab62aa566029ce25989ef7dc8e3634365f63 /net/sunrpc/svc_xprt.c | |
parent | c5b29f885afe890f953f7f23424045cdad31d3e4 (diff) | |
download | lwn-f16b6e8d838b2e2bb4561201311c66ac02ad67df.tar.gz lwn-f16b6e8d838b2e2bb4561201311c66ac02ad67df.zip |
sunrpc/cache: allow threads to block while waiting for cache update.
The current practice of waiting for cache updates by queueing the
whole request to be retried has (at least) two problems.
1/ With NFSv4, requests can be quite complex and re-trying a whole
request when a later part fails should only be a last-resort, not a
normal practice.
2/ Large requests, and in particular any 'write' request, will not be
queued by the current code and doing so would be undesirable.
In many cases only a very sort wait is needed before the cache gets
valid data.
So, providing the underlying transport permits it by setting
->thread_wait,
arrange to wait briefly for an upcall to be completed (as reflected in
the clearing of CACHE_PENDING).
If the short wait was not long enough and CACHE_PENDING is still set,
fall back on the old approach.
The 'thread_wait' value is set to 5 seconds when there are spare
threads, and 1 second when there are no spare threads.
These values are probably much higher than needed, but will ensure
some forward progress.
Note that as we only request an update for a non-valid item, and as
non-valid items are updated in place it is extremely unlikely that
cache_check will return -ETIMEDOUT. Normally cache_defer_req will
sleep for a short while and then find that the item is_valid.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc/svc_xprt.c')
-rw-r--r-- | net/sunrpc/svc_xprt.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index cbc084939dd8..8ff6840866fa 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -651,6 +651,11 @@ int svc_recv(struct svc_rqst *rqstp, long timeout) if (signalled() || kthread_should_stop()) return -EINTR; + /* Normally we will wait up to 5 seconds for any required + * cache information to be provided. + */ + rqstp->rq_chandle.thread_wait = 5*HZ; + spin_lock_bh(&pool->sp_lock); xprt = svc_xprt_dequeue(pool); if (xprt) { @@ -658,6 +663,12 @@ int svc_recv(struct svc_rqst *rqstp, long timeout) svc_xprt_get(xprt); rqstp->rq_reserved = serv->sv_max_mesg; atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved); + + /* As there is a shortage of threads and this request + * had to be queue, don't allow the thread to wait so + * long for cache updates. + */ + rqstp->rq_chandle.thread_wait = 1*HZ; } else { /* No data pending. Go to sleep */ svc_thread_enqueue(pool, rqstp); |