From: "Jürgen Groß" <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>, Dario Faggioli <dfaggioli@suse.com>
Cc: Charles Arnold <carnold@suse.com>, Glen <glenbarney@gmail.com>,
George Dunlap <george.dunlap@citrix.com>,
Tomas Mozes <hydrapolic@gmail.com>, Sarah Newman <srn@prgmr.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH 1/2] xen: credit2: avoid vCPUs to ever reach lower credits than idle
Date: Thu, 12 Mar 2020 17:00:23 +0100 [thread overview]
Message-ID: <21abe34e-54f0-70e3-d2f1-cf6984b5773a@suse.com> (raw)
In-Reply-To: <2e53ee4c-e2d9-f892-c8c3-62bff0c526ab@suse.com>
On 12.03.20 16:26, Jan Beulich wrote:
> On 12.03.2020 14:44, Dario Faggioli wrote:
>> --- a/xen/common/sched/credit2.c
>> +++ b/xen/common/sched/credit2.c
>> @@ -234,7 +234,7 @@
>> * units does not consume credits, and it must be lower than whatever
>> * amount of credit 'regular' unit would end up with.
>> */
>> -#define CSCHED2_IDLE_CREDIT (-(1U<<30))
>> +#define CSCHED2_IDLE_CREDIT INT_MIN
>
> The title saying "lower than", is "equal" actually fine? Looking
> at e.g. runq_insert() I'm getting the impression it's not.
>
> Looking at t2c_update() I'm also getting the impression that
> there's UB when the subtraction underflows. After all, if
> -1 << 30 wasn't small enough a value, I don't see why -1 << 31
> would be.
Yes, I'd limit svc->credit in t2c_update() to CSCHED2_IDLE_CREDIT+1
Juergen
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next prev parent reply other threads:[~2020-03-12 16:00 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 13:44 [Xen-devel] [PATCH 0/2] xen: credit2: fix vcpu starvation due to too few credits Dario Faggioli
2020-03-12 13:44 ` [Xen-devel] [PATCH 1/2] xen: credit2: avoid vCPUs to ever reach lower credits than idle Dario Faggioli
2020-03-12 13:55 ` Andrew Cooper
2020-03-12 14:40 ` George Dunlap
2020-03-12 15:10 ` Dario Faggioli
2020-03-12 14:58 ` Dario Faggioli
2020-03-12 14:45 ` George Dunlap
2020-03-12 17:03 ` Dario Faggioli
2020-03-12 15:26 ` Jan Beulich
2020-03-12 16:00 ` Jürgen Groß [this message]
2020-03-12 16:59 ` Dario Faggioli
2020-03-12 16:11 ` Dario Faggioli
2020-03-12 16:36 ` Jan Beulich
2020-03-12 13:44 ` [Xen-devel] [PATCH 2/2] xen: credit2: fix credit reset happening too few times Dario Faggioli
2020-03-12 15:08 ` [Xen-devel] [PATCH 0/2] xen: credit2: fix vcpu starvation due to too few credits Roger Pau Monné
2020-03-12 17:02 ` Dario Faggioli
2020-03-12 17:59 ` Roger Pau Monné
2020-03-13 6:19 ` Dario Faggioli
2020-03-12 15:51 ` Jürgen Groß
2020-03-12 16:27 ` Andrew Cooper
2020-03-13 7:26 ` Dario Faggioli
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