From: Vivek Goyal <vgoyal@redhat.com>
To: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: "cdupontd@redhat.com" <cdupontd@redhat.com>,
"Venegas Munoz,
Jose Carlos" <jose.carlos.venegas.munoz@intel.com>,
Greg Kurz <groug@kaod.org>,
qemu-devel@nongnu.org, virtio-fs-list <virtio-fs@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
"Shinde, Archana M" <archana.m.shinde@intel.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: Can not set high msize with virtio-9p (Was: Re: virtiofs vs 9p performance)
Date: Fri, 19 Feb 2021 14:01:12 -0500 [thread overview]
Message-ID: <20210219190112.GC3270@redhat.com> (raw)
In-Reply-To: <2709384.cAWMFGR5kF@silver>
On Fri, Feb 19, 2021 at 06:33:46PM +0100, Christian Schoenebeck wrote:
> On Freitag, 19. Februar 2021 17:08:48 CET Vivek Goyal wrote:
> > On Fri, Sep 25, 2020 at 10:06:41AM +0200, Christian Schoenebeck wrote:
> > > On Freitag, 25. September 2020 00:10:23 CEST Vivek Goyal wrote:
> > > > In my testing, with cache=none, virtiofs performed better than 9p in
> > > > all the fio jobs I was running. For the case of cache=auto for virtiofs
> > > > (with xattr enabled), 9p performed better in certain write workloads. I
> > > > have identified root cause of that problem and working on
> > > > HANDLE_KILLPRIV_V2 patches to improve WRITE performance of virtiofs
> > > > with cache=auto and xattr enabled.
> > >
> > > Please note, when it comes to performance aspects, you should set a
> > > reasonable high value for 'msize' on 9p client side:
> > > https://wiki.qemu.org/Documentation/9psetup#msize
> >
> > Hi Christian,
> >
> > I am not able to set msize to a higher value. If I try to specify msize
> > 16MB, and then read back msize from /proc/mounts, it sees to cap it
> > at 512000. Is that intended?
>
> 9p server side in QEMU does not perform any msize capping. The code in this
> case is very simple, it's just what you see in function v9fs_version():
>
> https://github.com/qemu/qemu/blob/6de76c5f324904c93e69f9a1e8e4fd0bd6f6b57a/hw/9pfs/9p.c#L1332
>
> > $ mount -t 9p -o trans=virtio,version=9p2000.L,cache=none,msize=16777216
> > hostShared /mnt/virtio-9p
> >
> > $ cat /proc/mounts | grep 9p
> > hostShared /mnt/virtio-9p 9p
> > rw,sync,dirsync,relatime,access=client,msize=512000,trans=virtio 0 0
> >
> > I am using 5.11 kernel.
>
> Must be something on client (guest kernel) side. I don't see this here with
> guest kernel 4.9.0 happening with my setup in a quick test:
>
> $ cat /etc/mtab | grep 9p
> svnRoot / 9p rw,dirsync,relatime,trans=virtio,version=9p2000.L,msize=104857600,cache=mmap 0 0
> $
>
> Looks like the root cause of your issue is this:
>
> struct p9_client *p9_client_create(const char *dev_name, char *options)
> {
> ...
> if (clnt->msize > clnt->trans_mod->maxsize)
> clnt->msize = clnt->trans_mod->maxsize;
>
> https://github.com/torvalds/linux/blob/f40ddce88593482919761f74910f42f4b84c004b/net/9p/client.c#L1045
That was introduced by a patch 2011.
commit c9ffb05ca5b5098d6ea468c909dd384d90da7d54
Author: Venkateswararao Jujjuri (JV) <jvrao@linux.vnet.ibm.com>
Date: Wed Jun 29 18:06:33 2011 -0700
net/9p: Fix the msize calculation.
msize represents the maximum PDU size that includes P9_IOHDRSZ.
You kernel 4.9 is newer than this. So most likely you have this commit
too. I will spend some time later trying to debug this.
Vivek
next prev parent reply other threads:[~2021-02-19 19:02 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 21:34 tools/virtiofs: Multi threading seems to hurt performance Vivek Goyal
2020-09-21 8:39 ` Stefan Hajnoczi
2020-09-21 13:39 ` Vivek Goyal
2020-09-21 16:57 ` Stefan Hajnoczi
2020-09-21 8:50 ` Dr. David Alan Gilbert
2020-09-21 13:35 ` Vivek Goyal
2020-09-21 14:08 ` Daniel P. Berrangé
2020-09-21 15:32 ` Dr. David Alan Gilbert
2020-09-22 10:25 ` Dr. David Alan Gilbert
2020-09-22 17:47 ` Vivek Goyal
2020-09-24 21:33 ` Venegas Munoz, Jose Carlos
2020-09-24 22:10 ` virtiofs vs 9p performance(Re: tools/virtiofs: Multi threading seems to hurt performance) Vivek Goyal
2020-09-25 8:06 ` virtiofs vs 9p performance Christian Schoenebeck
2020-09-25 13:13 ` Vivek Goyal
2020-09-25 15:47 ` Christian Schoenebeck
2021-02-19 16:08 ` Can not set high msize with virtio-9p (Was: Re: virtiofs vs 9p performance) Vivek Goyal
2021-02-19 17:33 ` Christian Schoenebeck
2021-02-19 19:01 ` Vivek Goyal [this message]
2021-02-20 15:38 ` Christian Schoenebeck
2021-02-22 12:18 ` Greg Kurz
2021-02-22 15:08 ` Christian Schoenebeck
2021-02-22 17:11 ` Greg Kurz
2021-02-23 13:39 ` Christian Schoenebeck
2021-02-23 14:07 ` Michael S. Tsirkin
2021-02-24 15:16 ` Christian Schoenebeck
2021-02-24 15:43 ` Dominique Martinet
2021-02-26 13:49 ` Christian Schoenebeck
2021-02-27 0:03 ` Dominique Martinet
2021-03-03 14:04 ` Christian Schoenebeck
2021-03-03 14:50 ` Dominique Martinet
2021-03-05 14:57 ` Christian Schoenebeck
2020-09-25 12:41 ` virtiofs vs 9p performance(Re: tools/virtiofs: Multi threading seems to hurt performance) Dr. David Alan Gilbert
2020-09-25 13:04 ` Christian Schoenebeck
2020-09-25 13:05 ` Dr. David Alan Gilbert
2020-09-25 16:05 ` Christian Schoenebeck
2020-09-25 16:33 ` Christian Schoenebeck
2020-09-25 18:51 ` Dr. David Alan Gilbert
2020-09-27 12:14 ` Christian Schoenebeck
2020-09-29 13:03 ` Vivek Goyal
2020-09-29 13:28 ` Christian Schoenebeck
2020-09-29 13:49 ` Vivek Goyal
2020-09-29 13:59 ` Christian Schoenebeck
2020-09-29 13:17 ` Vivek Goyal
2020-09-29 13:49 ` [Virtio-fs] " Miklos Szeredi
2020-09-29 14:01 ` Vivek Goyal
2020-09-29 14:54 ` Miklos Szeredi
2020-09-29 15:28 ` Vivek Goyal
2020-09-25 12:11 ` tools/virtiofs: Multi threading seems to hurt performance Dr. David Alan Gilbert
2020-09-25 13:11 ` Vivek Goyal
2020-09-21 20:16 ` Vivek Goyal
2020-09-22 11:09 ` Dr. David Alan Gilbert
2020-09-22 22:56 ` Vivek Goyal
2020-09-23 12:50 ` [Virtio-fs] " Chirantan Ekbote
2020-09-23 12:59 ` Vivek Goyal
2020-09-25 11:35 ` Dr. David Alan Gilbert
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