From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38543) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ayYqC-0000mM-Es for qemu-devel@nongnu.org; Fri, 06 May 2016 02:02:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ayYpz-0002YQ-M2 for qemu-devel@nongnu.org; Fri, 06 May 2016 02:02:14 -0400 MIME-Version: 1.0 In-Reply-To: <20160504174033.39faaada@bahia.huguette.org> References: <20160427083840.GA27160@igalia.com> <20160427191215.037c4c5c@bahia.huguette.org> <20160502145731.66bdcf27@bahia.huguette.org> <20160504174033.39faaada@bahia.huguette.org> Date: Fri, 6 May 2016 08:01:09 +0200 Message-ID: From: Pradeep Kiruvale Content-Type: multipart/alternative; boundary=089e0112c2de756fc70532262fe6 Subject: Re: [Qemu-devel] [Qemu-discuss] iolimits for virtio-9p List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz Cc: Alberto Garcia , qemu-devel@nongnu.org, "qemu-discuss@nongnu.org" --089e0112c2de756fc70532262fe6 Content-Type: text/plain; charset=UTF-8 On 4 May 2016 at 17:40, Greg Kurz wrote: > On Mon, 2 May 2016 17:49:26 +0200 > Pradeep Kiruvale wrote: > > > On 2 May 2016 at 14:57, Greg Kurz wrote: > > > > > On Thu, 28 Apr 2016 11:45:41 +0200 > > > Pradeep Kiruvale wrote: > > > > > > > On 27 April 2016 at 19:12, Greg Kurz > wrote: > > > > > > > > > On Wed, 27 Apr 2016 16:39:58 +0200 > > > > > Pradeep Kiruvale wrote: > > > > > > > > > > > On 27 April 2016 at 10:38, Alberto Garcia > wrote: > > > > > > > > > > > > > On Wed, Apr 27, 2016 at 09:29:02AM +0200, Pradeep Kiruvale > wrote: > > > > > > > > > > > > > > > Thanks for the reply. I am still in the early phase, I will > let > > > you > > > > > > > > know if any changes are needed for the APIs. > > > > > > > > > > > > > > > > We might also have to implement throttle-group.c for 9p > devices, > > > if > > > > > > > > we want to apply throttle for group of devices. > > > > > > > > > > > > > > Fair enough, but again please note that: > > > > > > > > > > > > > > - throttle-group.c is not meant to be generic, but it's tied to > > > > > > > BlockDriverState / BlockBackend. > > > > > > > - it is currently being rewritten: > > > > > > > > > > https://lists.gnu.org/archive/html/qemu-block/2016-04/msg00645.html > > > > > > > > > > > > > > If you can explain your use case with a bit more detail we can > try > > > to > > > > > > > see what can be done about it. > > > > > > > > > > > > > > > > > > > > We want to use virtio-9p for block io instead of virtio-blk-pci. > > > But in > > > > > > case of > > > > > > > > > > 9p is mostly aimed at sharing files... why would you want to use > it for > > > > > block io instead of a true block device ? And how would you do > that ? > > > > > > > > > > > > > *Yes, we want to share the files itself. So we are using the > virtio-9p.* > > > > > > You want to pass a disk image to the guest as a plain file on a 9p > mount ? > > > And then, what do you do in the guest ? Attach it to a loop device ? > > > > > > > Yes, would like to mount as a 9p drive and create file inside that and > > read/write. > > This was the experiment we are doing, actual use case no idea. My work is > > to do > > a feasibility test does it work or not. > > > > > > > > > > > *We want to have QoS on these files access for every VM.* > > > > > > > > > > You won't be able to have QoS on selected files, but it may be > possible to > > > introduce limits at the fsdev level: control all write accesses to all > > > files > > > and all read accesses to all files for a 9p device. > > > > > > > That is right, I do not want to have QoS for individual files but to > whole > > fsdev device. > > > > > > > > > > > > > > > > > > > virtio-9p we can just use fsdev devices, so we want to apply > > > throttling > > > > > > (QoS) > > > > > > on these devices and as of now the io throttling only possible > with > > > the > > > > > > -drive option. > > > > > > > > > > > > > > > > Indeed. > > > > > > > > > > > As a work around we are doing the throttling using cgroup. It has > > > its own > > > > > > costs. > > > > > > > > > > Can you elaborate ? > > > > > > > > > > > > > *We saw that we need to create cgroups and set it and also we > observed > > > lot > > > > of iowaits * > > > > *compared to implementing the throttling inside the qemu.* > > > > *This we did observe by using the virtio-blk-pci devices. (Using > cgroups > > > Vs > > > > qemu throttling)* > > > > > > > > > > > > > > > > > Just to be sure I get it right. > > > > > > You tried both: > > > 1) run QEMU with -device virtio-blk-pci and -drive throttling.* > > > 2) run QEMU with -device virtio-blk-pci in its own cgroup > > > > > > And 1) has better performance and is easier to use than 2) ? > > > > > > And what do you expect with 9p compared to 1) ? > > > > > > > > That was just to understand the cost of cpu > > io throttling inside the qemu vs using cgroup. > > > > The bench-marking we did to reproduce the numbers and understand the cost > > mentioned in > > > > > http://www.linux-kvm.org/images/7/72/2011-forum-keep-a-limit-on-it-io-throttling-in-qemu.pdf > > > > Thanks, > > Pradeep > > > > Ok. So you did compare current QEMU block I/O throttling with cgroup ? And > you observed numbers > similar to the link above ? > *Yes, I did, I did run DD command in guest to do IO. The recent QEMU is in par with cgroups in terms * *of CPU utilization.* > > And now you would like to run the same test on a file in a 9p mount with > experimental 9p QoS ? > > *Yes, you are right.* > Maybe possible to reuse the throttle.h API and hack v9fs_write() and > v9fs_read() in 9p.c then. > > *OK, I am looking into it. Are there any sample test cases or something about how to apply the* *throttling APIs to a device?* Regards, Pradeep > Cheers. > > -- > Greg > > > > > > > > > > > Thanks, > > > > Pradeep > > > > > > > > > --089e0112c2de756fc70532262fe6 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On 4 May 2016 at 17:40, Greg Kurz <gkurz@linux.vnet.ibm.com= > wrote:
On Mon, 2 May 2016 17:49:26 +0200
Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:

> On 2 May 2016 at 14:57, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
>
> > On Thu, 28 Apr 2016 11:45:41 +0200
> > Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:
> >
> > > On 27 April 2016 at 19:12, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
> > >
> > > > On Wed, 27 Apr 2016 16:39:58 +0200
> > > > Pradeep Kiruvale <pradeepkiruvale@gmail.com> wrote:
> > > >
> > > > > On 27 April 2016 at 10:38, Alberto Garcia <berto@igalia.com> wrote:
> > > > >
> > > > > > On Wed, Apr 27, 2016 at 09:29:02AM +0200, Pra= deep Kiruvale wrote:
> > > > > >
> > > > > > > Thanks for the reply. I am still in the = early phase, I will let
> > you
> > > > > > > know if any changes are needed for the A= PIs.
> > > > > > >
> > > > > > > We might also have to implement throttle= -group.c for 9p devices,
> > if
> > > > > > > we want to apply throttle for group of d= evices.
> > > > > >
> > > > > > Fair enough, but again please note that:
> > > > > >
> > > > > > - throttle-group.c is not meant to be generic= , but it's tied to
> > > > > >=C2=A0 =C2=A0BlockDriverState / BlockBackend.<= br> > > > > > > - it is currently being rewritten:
> > > > > >
> > https://lists.gnu.org/a= rchive/html/qemu-block/2016-04/msg00645.html
> > > > > >
> > > > > > If you can explain your use case with a bit m= ore detail we can try
> > to
> > > > > > see what can be done about it.
> > > > > >
> > > > > >
> > > > > We want to use=C2=A0 virtio-9p for block io instea= d of virtio-blk-pci.
> > But in
> > > > > case of
> > > >
> > > > 9p is mostly aimed at sharing files... why would you wa= nt to use it for
> > > > block io instead of a true block device ? And how would= you do that ?
> > > >
> > >
> > > *Yes, we want to share the files itself. So we are using the= virtio-9p.*
> >
> > You want to pass a disk image to the guest as a plain file on a 9= p mount ?
> > And then, what do you do in the guest ? Attach it to a loop devic= e ?
> >
>
> Yes, would like to mount as=C2=A0 a 9p drive and create file inside th= at and
> read/write.
> This was the experiment we are doing, actual use case no idea. My work= is
> to do
> a feasibility test does it work or not.
>
>
> >
> > > *We want to have QoS on these files access for every VM.* > > >
> >
> > You won't be able to have QoS on selected files, but it may b= e possible to
> > introduce limits at the fsdev level: control all write accesses t= o all
> > files
> > and all read accesses to all files for a 9p device.
> >
>
> That is right, I do not want to have QoS for individual files but to w= hole
> fsdev device.
>
>
> > >
> > > >
> > > > > virtio-9p we can just use fsdev devices, so we wan= t to apply
> > throttling
> > > > > (QoS)
> > > > > on these devices and as of now the io throttling o= nly possible with
> > the
> > > > > -drive option.
> > > > >
> > > >
> > > > Indeed.
> > > >
> > > > > As a work around we are doing the throttling using= cgroup. It has
> > its own
> > > > > costs.
> > > >
> > > > Can you elaborate ?
> > > >
> > >
> > > *We saw that we need to create cgroups and set it and also w= e observed
> > lot
> > > of iowaits *
> > > *compared to implementing the throttling inside the qemu.* > > > *This we did observe by using the virtio-blk-pci devices. (U= sing cgroups
> > Vs
> > > qemu throttling)*
> > >
> >
>
>
> >
> > Just to be sure I get it right.
> >
> > You tried both:
> > 1) run QEMU with -device virtio-blk-pci and -drive throttling.* > > 2) run QEMU with -device virtio-blk-pci in its own cgroup
> >
> > And 1) has better performance and is easier to use than 2) ?
> >
> > And what do you expect with 9p compared to 1) ?
> >
> >
> That was just to understand the cost of cpu
>=C2=A0 io throttling inside the qemu vs using cgroup.
>
> The bench-marking we did to reproduce the numbers and understand the c= ost
> mentioned in
>
> htt= p://www.linux-kvm.org/images/7/72/2011-forum-keep-a-limit-on-it-io-throttli= ng-in-qemu.pdf
>
> Thanks,
> Pradeep
>

Ok. So you did compare current QEMU block I/O throttling with c= group ? And you observed numbers
similar to the link above ?

Y= es, I did, I did run DD command in guest to do IO. The recent QEMU is in pa= r with cgroups in terms=C2=A0
of CPU utilization.

And now you would like to run the same test on a file in a 9p mount with ex= perimental 9p QoS ?

Yes, you are right.
=C2=A0
Maybe possible to reuse the throttle.h API and hack v9fs_write() and v9fs_r= ead() in 9p.c then.


OK, I am looking into it. Are there= any sample test cases or something about how to apply the
throttling APIs to a device?


R= egards,
Pradeep

=C2=A0
Cheers.

--
Greg

>
> > >
> > > Thanks,
> > > Pradeep
> >
> >



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