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Date: Wed, 13 May 2009 10:58:39 -0400
From: Jeff Moyer <jmoyer@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
"Rafael J. Wysocki" <rjw@...k.pl>,
Olga Kornievskaia <aglo@...i.umich.edu>,
"J. Bruce Fields" <bfields@...ldses.org>,
Jim Rees <rees@...ch.edu>, linux-nfs@...r.kernel.org
Subject: Re: 2.6.30-rc deadline scheduler performance regression for iozone over NFS
Andrew Morton <akpm@...ux-foundation.org> writes:
> (obvious cc's added...)
>
> It's an iozone performance regression.
>
> On Tue, 12 May 2009 23:29:30 -0400 Jeff Moyer <jmoyer@...hat.com> wrote:
>
>> Jens Axboe <jens.axboe@...cle.com> writes:
>>
>> > On Mon, May 11 2009, Jeff Moyer wrote:
>> >> Jens Axboe <jens.axboe@...cle.com> writes:
>> >>
>> >> > On Fri, May 08 2009, Andrew Morton wrote:
>> >> >> On Thu, 23 Apr 2009 10:01:58 -0400
>> >> >> Jeff Moyer <jmoyer@...hat.com> wrote:
>> >> >>
>> >> >> > Hi,
>> >> >> >
>> >> >> > I've been working on CFQ improvements for interleaved I/Os between
>> >> >> > processes, and noticed a regression in performance when using the
>> >> >> > deadline I/O scheduler. The test uses a server configured with a cciss
>> >> >> > array and 1Gb/s ethernet.
>> >> >> >
>> >> >> > The iozone command line was:
>> >> >> > iozone -s 2000000 -r 64 -f /mnt/test/testfile -i 1 -w
>> >> >> >
>> >> >> > The numbers in the nfsd's row represent the number of nfsd "threads".
>> >> >> > These numbers (in MB/s) represent the average of 5 runs.
>> >> >> >
>> >> >> > v2.6.29
>> >> >> >
>> >> >> > nfsd's | 1 | 2 | 4 | 8
>> >> >> > --------+---------------+-------+------
>> >> >> > deadline| 43207 | 67436 | 96289 | 107590
>> >> >> >
>> >> >> > 2.6.30-rc1
>> >> >> >
>> >> >> > nfsd's | 1 | 2 | 4 | 8
>> >> >> > --------+---------------+-------+------
>> >> >> > deadline| 43732 | 68059 | 76659 | 83231
>> >> >> >
>> >> >> > 2.6.30-rc3.block-for-linus
>> >> >> >
>> >> >> > nfsd's | 1 | 2 | 4 | 8
>> >> >> > --------+---------------+-------+------
>> >> >> > deadline| 46102 | 71151 | 83120 | 82330
>> >> >> >
>> >> >> >
>> >> >> > Notice the drop for 4 and 8 threads. It may be worth noting that the
>> >> >> > default number of NFSD threads is 8.
Just following up with numbers:
2.6.30-rc4
nfsd's | 8
--------+------
cfq | 51632 (49791 52436 52308 51488 52141)
deadline| 65558 (41675 42559 74820 87518 81221)
2.6.30-rc4 reverting the sunrpc "fix"
nfsd's | 8
--------+------
cfq | 82513 (81650 82762 83147 82935 82073)
deadline| 107827 (109730 106077 107175 108524 107632)
The numbers in parenthesis are the individual runs. Notice how
2.6.30-rc4 has some pretty wide variations for deadline.
Cheers,
Jeff
>> >> >> I guess we should ask Rafael to add this to the post-2.6.29 regression
>> >> >> list.
>> >> >
>> >> > I agree. It'd be nice to bisect this one down, I'm guessing some mm
>> >> > change has caused this writeout regression.
>> >>
>> >> It's not writeout, it's a read test.
>> >
>> > Doh sorry, I even ran these tests as well a few weeks back. So perhaps
>> > some read-ahead change, I didn't look into it. FWIW, on a single SATA
>> > drive here, it didn't show any difference.
>>
>> OK, I bisected this to the following commit. The mount is done using
>> NFSv3, by the way.
>>
>> commit 47a14ef1af48c696b214ac168f056ddc79793d0e
>> Author: Olga Kornievskaia <aglo@...i.umich.edu>
>> Date: Tue Oct 21 14:13:47 2008 -0400
>>
>> svcrpc: take advantage of tcp autotuning
>>
>> Allow the NFSv4 server to make use of TCP autotuning behaviour, which
>> was previously disabled by setting the sk_userlocks variable.
>>
>> Set the receive buffers to be big enough to receive the whole RPC
>> request, and set this for the listening socket, not the accept socket.
>>
>> Remove the code that readjusts the receive/send buffer sizes for the
>> accepted socket. Previously this code was used to influence the TCP
>> window management behaviour, which is no longer needed when autotuning
>> is enabled.
>>
>> This can improve IO bandwidth on networks with high bandwidth-delay
>> products, where a large tcp window is required. It also simplifies
>> performance tuning, since getting adequate tcp buffers previously
>> required increasing the number of nfsd threads.
>>
>> Signed-off-by: Olga Kornievskaia <aglo@...i.umich.edu>
>> Cc: Jim Rees <rees@...ch.edu>
>> Signed-off-by: J. Bruce Fields <bfields@...i.umich.edu>
>>
>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>> index 5763e64..7a2a90f 100644
>> --- a/net/sunrpc/svcsock.c
>> +++ b/net/sunrpc/svcsock.c
>> @@ -345,7 +345,6 @@ static void svc_sock_setbufsize(struct socket *sock, unsigned int snd,
>> lock_sock(sock->sk);
>> sock->sk->sk_sndbuf = snd * 2;
>> sock->sk->sk_rcvbuf = rcv * 2;
>> - sock->sk->sk_userlocks |= SOCK_SNDBUF_LOCK|SOCK_RCVBUF_LOCK;
>> release_sock(sock->sk);
>> #endif
>> }
>> @@ -797,23 +796,6 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
>> test_bit(XPT_CONN, &svsk->sk_xprt.xpt_flags),
>> test_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags));
>>
>> - if (test_and_clear_bit(XPT_CHNGBUF, &svsk->sk_xprt.xpt_flags))
>> - /* sndbuf needs to have room for one request
>> - * per thread, otherwise we can stall even when the
>> - * network isn't a bottleneck.
>> - *
>> - * We count all threads rather than threads in a
>> - * particular pool, which provides an upper bound
>> - * on the number of threads which will access the socket.
>> - *
>> - * rcvbuf just needs to be able to hold a few requests.
>> - * Normally they will be removed from the queue
>> - * as soon a a complete request arrives.
>> - */
>> - svc_sock_setbufsize(svsk->sk_sock,
>> - (serv->sv_nrthreads+3) * serv->sv_max_mesg,
>> - 3 * serv->sv_max_mesg);
>> -
>> clear_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
>>
>> /* Receive data. If we haven't got the record length yet, get
>> @@ -1061,15 +1043,6 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
>>
>> tcp_sk(sk)->nonagle |= TCP_NAGLE_OFF;
>>
>> - /* initialise setting must have enough space to
>> - * receive and respond to one request.
>> - * svc_tcp_recvfrom will re-adjust if necessary
>> - */
>> - svc_sock_setbufsize(svsk->sk_sock,
>> - 3 * svsk->sk_xprt.xpt_server->sv_max_mesg,
>> - 3 * svsk->sk_xprt.xpt_server->sv_max_mesg);
>> -
>> - set_bit(XPT_CHNGBUF, &svsk->sk_xprt.xpt_flags);
>> set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
>> if (sk->sk_state != TCP_ESTABLISHED)
>> set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
>> @@ -1140,8 +1113,14 @@ static struct svc_sock *svc_setup_socket(struct svc_serv *serv,
>> /* Initialize the socket */
>> if (sock->type == SOCK_DGRAM)
>> svc_udp_init(svsk, serv);
>> - else
>> + else {
>> + /* initialise setting must have enough space to
>> + * receive and respond to one request.
>> + */
>> + svc_sock_setbufsize(svsk->sk_sock, 4 * serv->sv_max_mesg,
>> + 4 * serv->sv_max_mesg);
>> svc_tcp_init(svsk, serv);
>> + }
>>
>> /*
>> * We start one listener per sv_serv. We want AF_INET
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