> On Jun 21, 2023, at 5:28 PM, Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hello, > > On Wed, Jun 21, 2023 at 03:26:22PM +0000, Chuck Lever III wrote: >> lock_stat reports that the pool->lock kernel/workqueue.c:1483 is the highest >> contended lock on my test NFS client. The issue appears to be that the three >> NFS-related workqueues, rpciod_workqueue, xprtiod_workqueue, and nfsiod all >> get placed in the same worker_pool, so they have to fight over one pool lock. >> >> I notice that ib_comp_wq is allocated with the same flags, but I don't see >> significant contention there, and a trace_printk in __queue_work shows that >> work items queued on that WQ seem to alternate between at least two different >> worker_pools. >> >> Is there a preferred way to ensure the NFS WQs get spread a little more fairly >> amongst the worker_pools? > > Can you share the output of lstopo on the test machine? > > The following branch has pending workqueue changes which makes unbound > workqueues finer grained by default and a lot more flexible in how they're > segmented. > > git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git affinity-scopes-v2 > > Can you please test with the brnach? If the default doesn't improve the > situation, you can set WQ_SYSFS on the affected workqueues and change their > scoping by writing to /sys/devices/virtual/WQ_NAME/affinity_scope. Please > take a look at > > https://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git/tree/Documentation/core-api/workqueue.rst?h=affinity-scopes-v2#n350 > > for more details. The good news: On stock 6.4-rc7: fio 8k [r=108k,w=46.9k IOPS] On the affinity-scopes-v2 branch (with no other tuning): fio 8k [r=130k,w=55.9k IOPS] The bad news: pool->lock is still the hottest lock on the system during the test. I'll try some of the alternate scope settings this afternoon. -- Chuck Lever
