On Mon, 2023-07-10 at 12:41 -0400, Chuck Lever wrote: > Walking a linked list to find an idle thread is not CPU cache- > friendly, and in fact I've noted palpable per-request latency > impacts as the number of nfsd threads on the server increases. > > After discussing some possible improvements with Jeff at LSF/MM, > I've been experimenting with the following series. I've measured an > order of magnitude latency improvement in the thread lookup time, > and have managed to keep the whole thing lockless. > > This version of the series addresses Neil's earlier comments and > is robust under load. The first 7 patches in this series seem > uncontroversial, so I'll push them to the > "topic-sunrpc-thread-scheduling" branch of: > > https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git > > The last two are still under discussion. They are posted as part > of this series for comparison to other proposals, but are not yet > included in the topic branch. But they are tested and working. > > > Changes since v2: > * Dropped the patch that converts sp_lock to a simple spinlock > * Replaced explicit memory barriers in svc_get_next_xprt() > * Select thread victims from the other end of the bitmap > * Added a metric for wake-ups that find nothing on the transport queue > > Changes since RFC: > * Add a counter for ingress RPC messages > * Add a few documenting comments > * Move the more controversial patches to the end of the series > * Clarify the refactoring of svc_wake_up() > * Increase the value of RPCSVC_MAXPOOLTHREADS to 4096 (and tested with that many threads) > * Optimize the loop in svc_pool_wake_idle_thread() > * Optimize marking a thread "idle" in svc_get_next_xprt() > > --- > > Chuck Lever (9): > SUNRPC: Deduplicate thread wake-up code > SUNRPC: Report when no service thread is available. > SUNRPC: Split the svc_xprt_dequeue tracepoint > SUNRPC: Count ingress RPC messages per svc_pool > SUNRPC: Count pool threads that were awoken but found no work to do > SUNRPC: Clean up svc_set_num_threads > SUNRPC: Replace dprintk() call site in __svc_create() > SUNRPC: Replace sp_threads_all with an xarray > SUNRPC: Convert RQ_BUSY into a per-pool bitmap > > > fs/nfsd/nfssvc.c | 3 +- > include/linux/sunrpc/svc.h | 19 ++-- > include/trace/events/sunrpc.h | 159 ++++++++++++++++++++++++++---- > net/sunrpc/svc.c | 177 ++++++++++++++++++++++------------ > net/sunrpc/svc_xprt.c | 99 ++++++++++--------- > 5 files changed, 323 insertions(+), 134 deletions(-) > > -- > Chuck Lever > You can add my Reviewed-by to the first 7 patches. The last two are not quite there yet, I think, but I like how they're looking so far. Cheers, -- Jeff Layton <jlayton@xxxxxxxxxx>
