|Summary:||2.6.30-rc deadline scheduler performance regression for iozone over NFS|
|Product:||File System||Reporter:||Rafael J. Wysocki (rjw)|
|Bug Depends on:|
SUNRPC: Fix the TCP server's send buffer accounting
SUNRPC: Fix the TCP write space reservations for deferred requests
SUNRPC: Fix svc_tcp_recvfrom()
Description Rafael J. Wysocki 2009-05-16 21:18:14 UTC
Subject : 2.6.30-rc deadline scheduler performance regression for iozone over NFS Submitter : Jeff Moyer <email@example.com> Date : 2009-04-23 14:01 References : http://marc.info/?l=linux-kernel&m=124049547915450&w=4 Notify-Also : Jens Axboe <firstname.lastname@example.org> Notify-Also : Olga Kornievskaia <email@example.com> Notify-Also : Jim Rees <firstname.lastname@example.org> Notify-Also : Trond Myklebust <email@example.com> Notify-Also : "J. Bruce Fields" <firstname.lastname@example.org> This entry is being used for tracking a regression from 2.6.29. Please don't close it until the problem is fixed in the mainline.
Comment 1 Jens Axboe 2009-05-18 08:22:48 UTC
Reassign to Trond, this is a nfs regression, not block layer.
Comment 2 Trond Myklebust 2009-05-19 20:22:24 UTC
Reassigning to Bruce, since this is a server regression rather than a client issue :-)
Comment 3 Trond Myklebust 2009-05-19 20:28:24 UTC
Created attachment 21433 [details] SUNRPC: Fix the TCP server's send buffer accounting Currently, the sunrpc server is refusing to allow us to process new RPC calls if the TCP send buffer is 2/3 full, even if we do actually have enough free space to guarantee that we can send another request. The following patch fixes svc_tcp_has_wspace() so that we only stop processing requests if we know that the socket buffer cannot possibly fit another reply. It also fixes the tcp write_space() callback so that we only clear the SOCK_NOSPACE flag when the TCP send buffer is less than 2/3 full. This should ensure that the send window will grow as per the standard TCP socket code.
Comment 4 Trond Myklebust 2009-05-19 20:29:01 UTC
Created attachment 21434 [details] SUNRPC: Fix the TCP write space reservations for deferred requests Ensure that deferred requests are accounted for correctly by the write space reservation mechanism. In order to avoid double counting, remove the reservation when we defer the request, and save any calculated value, so that we can restore it when the request is requeued.
Comment 5 Trond Myklebust 2009-05-19 20:29:37 UTC
Created attachment 21435 [details] SUNRPC: Fix svc_tcp_recvfrom() Ensure that we immediately read and buffer data from the incoming TCP stream so that we grow the receive window quickly, and don't deadlock on large READ or WRITE requests.
Comment 6 Trond Myklebust 2009-05-29 21:20:42 UTC
The offending commit has been reverted in 2.6.30-rc... Closing bug