From: Dario Faggioli <dario.faggioli@citrix.com>
To: Jan Beulich <JBeulich@suse.com>, Chong Li <lichong659@gmail.com>
Cc: Chong Li <chong.li@wustl.edu>, Sisu Xi <xisisu@gmail.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
xen-devel <xen-devel@lists.xen.org>,
Meng Xu <mengxu@cis.upenn.edu>,
Dagaen Golomb <dgolomb@seas.upenn.edu>
Subject: Re: [PATCH v6 for Xen 4.7 1/4] xen: enable per-VCPU parameter settings for RTDS scheduler
Date: Mon, 7 Mar 2016 18:53:01 +0100 [thread overview]
Message-ID: <1457373181.3102.74.camel@citrix.com> (raw)
In-Reply-To: <56DDBCFF02000078000DA1A0@prv-mh.provo.novell.com>
[-- Attachment #1.1: Type: text/plain, Size: 5062 bytes --]
On Mon, 2016-03-07 at 09:40 -0700, Jan Beulich wrote:
> > > > On 07.03.16 at 17:28, <lichong659@gmail.com> wrote:
> > On Mon, Mar 7, 2016 at 6:59 AM, Jan Beulich <JBeulich@suse.com>
> > wrote:
> > >
> > > > @@ -1163,6 +1173,96 @@ rt_dom_cntl(
> > > >
> > > > + case XEN_DOMCTL_SCHEDOP_getvcpuinfo:
> > > > + if ( guest_handle_is_null(op->u.v.vcpus) )
> > > > + {
> > > > + rc = -EINVAL;
> > > Perhaps rather -EFAULT? But then again - what is this check good
> > > for
> > > (considering that it doesn't cover other obviously bad handle
> > > values)?
> > Dario suggested this in the last post, because vcpus is a handle
> > and
> > needs to be validated.
>
> Well, as said - the handle being non-null doesn't make it a valid
> handle. Any validation can be left to copy_{to,from}_guest*()
> unless you mean to give a null handle some special meaning.
>
IIRC, I was looking at how XEN_SYSCTL_pcitopoinfo is handled, for
reference, and that has some guest_handle_is_null()==>EINVAL sainity
checking (in xen/common/sysctl.c), which, when I thought about it, made
sense to me.
My reasoning was, sort of:
1. if the handle is NULL, no point getting into the somewhat
complicated logic of the while,
2. more accurate error reporting: as being passed a NULL handler
looked something we could identify and call invalid, rather than
waiting for the copy to fault.
In any event, I've no problem at all with this being dropped.
> > > > + {
> > > > + rc = -EINVAL;
> > > > + break;
> > > > + }
> > > > +
> > > > + spin_lock_irqsave(&prv->lock, flags);
> > > > + svc = rt_vcpu(d->vcpu[local_sched.vcpuid]);
> > > > + local_sched.s.rtds.budget = svc->budget /
> > > > MICROSECS(1);
> > > > + local_sched.s.rtds.period = svc->period /
> > > > MICROSECS(1);
> > > > + spin_unlock_irqrestore(&prv->lock, flags);
> > > > +
> > > > + if ( __copy_to_guest_offset(op->u.v.vcpus, index,
> > > > + &local_sched, 1) )
> > > > + {
> > > > + rc = -EFAULT;
> > > > + break;
> > > > + }
> > > > + if ( (++index > 0x3f) && hypercall_preempt_check()
> > > > )
> > > > + break;
> > > So how is the caller going to be able to reliably read all vCPU-
> > > s'
> > > information for a guest with more than 64 vCPU-s?
> > In libxc, we re-issue hypercall if the current one is preempted.
> And with the current code - how does libxc know? (And anyway,
> this should only be a last resort, if the hypervisor can't by itself
> arrange for a continuation. If done this way, having a code
> comment referring to the required caller behavior would seem to
> be an absolute must.)
>
I definitely agree on commenting.
About the structure of the code, as said above, I do like
how XEN_SYSCTL_pcitopoinfo ended up being handled, I think it is a
great fit for this specific case and, comparing at both this and
previous version, I do think this one is (bugs apart) looking better.
I'm sure I said this --long ago-- when discussing v4 (and maybe even
previous versions), as well as more recently, when reviewing v5, and
that's why Chong (finally! :-D) did it.
So, with the comment in place (and with bugs fixed :-)), are you (Jan)
ok with this being done this way?
> > > > + }
> > > > +
> > > > + if ( !rc && (op->u.v.nr_vcpus != index) )
> > > > + op->u.v.nr_vcpus = index;
> > > I don't think the right side of the && is really necessary /
> > > useful.
> > The right side is to check whether the vcpus array is fully
> > processed.
> > When it is true and no error occurs (rc == 0), we
> > update op->u.v.nr_vcpus, which is returned to libxc, and helps xc
> > function figuring out how many un-processed vcpus should
> > be taken care of in the next hypercall.
> Just consider what the contents of op->u.v.nr_vcpus is after
> this piece of code was executed, once with the full conditional,
> and another time with the right side of the && omitted.
>
BTW, Chong, I'm not sure this has to do with what Jan is saying, but
looking again at XEN_SYSCTL_pcitopoinfo, it looks to me you're missing
copying nr_vcpus back up to the guest (which is actually what makes
libxc knows whether all vcpus have been processed or now).
Regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
[-- Attachment #1.2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 181 bytes --]
[-- Attachment #2: Type: text/plain, Size: 126 bytes --]
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-03-07 17:53 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-06 17:55 [PATCH v6 for Xen 4.7 0/4] Enable per-VCPU parameter settings for RTDS scheduler Chong Li
2016-03-06 17:55 ` [PATCH v6 for Xen 4.7 1/4] xen: enable " Chong Li
2016-03-07 12:59 ` Jan Beulich
2016-03-07 16:28 ` Chong Li
2016-03-07 16:40 ` Jan Beulich
2016-03-07 17:53 ` Dario Faggioli [this message]
2016-03-07 22:16 ` Chong Li
2016-03-08 9:10 ` Jan Beulich
2016-03-08 10:34 ` Dario Faggioli
2016-03-08 11:47 ` Jan Beulich
2016-03-08 19:09 ` Wei Liu
2016-03-09 16:10 ` Dario Faggioli
2016-03-09 16:38 ` Jan Beulich
2016-03-13 17:05 ` Chong Li
2016-03-14 8:37 ` Jan Beulich
2016-03-14 9:10 ` Dario Faggioli
2016-03-14 9:15 ` Jan Beulich
2016-03-14 10:05 ` Dario Faggioli
2016-03-15 16:22 ` Chong Li
2016-03-15 16:41 ` Dario Faggioli
2016-03-15 17:22 ` Chong Li
2016-03-16 3:14 ` Meng Xu
2016-03-16 3:32 ` Chong Li
2016-03-16 3:43 ` Meng Xu
2016-03-16 8:23 ` Dario Faggioli
2016-03-16 14:37 ` Meng Xu
2016-03-16 14:46 ` Chong Li
2016-03-16 14:53 ` Dario Faggioli
2016-03-16 14:46 ` Chong Li
2016-03-16 14:54 ` Dario Faggioli
2016-03-16 10:48 ` Jan Beulich
2016-03-10 22:35 ` Chong Li
2016-03-10 22:50 ` Wei Liu
2016-03-14 9:07 ` Dario Faggioli
2016-03-06 17:55 ` [PATCH v6 for Xen 4.7 2/4] libxc: " Chong Li
2016-03-08 19:09 ` Wei Liu
2016-03-08 19:32 ` Chong Li
2016-03-08 19:36 ` Wei Liu
2016-03-06 17:55 ` [PATCH v6 for Xen 4.7 3/4] libxl: " Chong Li
2016-03-08 19:12 ` Wei Liu
2016-03-09 0:38 ` Chong Li
2016-03-09 14:01 ` Wei Liu
2016-03-09 17:28 ` Dario Faggioli
2016-03-09 21:57 ` Chong Li
2016-03-09 17:09 ` Dario Faggioli
2016-03-09 17:28 ` Dario Faggioli
2016-03-06 17:55 ` [PATCH v6 for Xen 4.7 4/4] xl: " Chong Li
2016-03-08 19:12 ` Wei Liu
2016-03-08 21:24 ` Chong Li
2016-03-09 14:01 ` Wei Liu
2016-03-09 14:09 ` Wei Liu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1457373181.3102.74.camel@citrix.com \
--to=dario.faggioli@citrix.com \
--cc=JBeulich@suse.com \
--cc=chong.li@wustl.edu \
--cc=dgolomb@seas.upenn.edu \
--cc=george.dunlap@eu.citrix.com \
--cc=lichong659@gmail.com \
--cc=mengxu@cis.upenn.edu \
--cc=xen-devel@lists.xen.org \
--cc=xisisu@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).