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Fri, 12 Jun 2020 15:55:11 -0700 (PDT) MIME-Version: 1.0 References: <20200612002205.174295-1-volodymyr_babchuk@epam.com> <20200612002205.174295-2-volodymyr_babchuk@epam.com> <0ce0bbf8-fd15-e87b-727c-56dd7c09cdcb@suse.com> <7ec7b6568afb3df41f8407015c198b1ccb341c5b.camel@epam.com> <5bd54018f5e045816d25f686124395a1f27a2122.camel@epam.com> <51fce146-f2bd-6098-bef9-2fd925ec7f96@xen.org> <0fc7034d696bbc601ccf2bd563ef9fb435499eea.camel@suse.com> In-Reply-To: <0fc7034d696bbc601ccf2bd563ef9fb435499eea.camel@suse.com> From: Julien Grall Date: Fri, 12 Jun 2020 23:54:59 +0100 Message-ID: Subject: Re: [RFC PATCH v1 1/6] sched: track time spent in IRQ handler To: Dario Faggioli Content-Type: text/plain; charset="UTF-8" X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: "jgross@suse.com" , "sstabellini@kernel.org" , "wl@xen.org" , "andrew.cooper3@citrix.com" , "ian.jackson@eu.citrix.com" , "george.dunlap@citrix.com" , "jbeulich@suse.com" , "xen-devel@lists.xenproject.org" , Volodymyr Babchuk , "roger.pau@citrix.com" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Fri, 12 Jun 2020 at 21:08, Dario Faggioli wrote: > > On Fri, 2020-06-12 at 13:21 +0100, Julien Grall wrote: > > On 12/06/2020 12:33, Volodymyr Babchuk wrote: > > > On Fri, 2020-06-12 at 12:29 +0100, Julien Grall wrote: > > > > > Basically, this value holds time span between calls to > > > > > schedule(). This > > > > > variable gets zeroed out every time scheduler requests for time > > > > > adjustment value. So, it should not depend on total VM run > > > > > time. > > > > This is assuming that the scheduler will be called. With the NULL > > > > scheduler in place, there is a fair chance this may never be > > > > called. > > > > > > > Yeah, this is a good point. I mean, I wouldn't be sure about "never", > as even there, we'd probably have softirqs, tasklets, etc... And I > still have to look at these patches in more details to figure out > properly whether they'd help for this. Unlike x86, Xen doesn't prod another pCPU consistently. :) This was already discussed in multiple threads in the past (see [1] which not resolved yet). So yes, I am pretty confident I can recreate a case where the scheduling function may never be called on Arm :). Cheers, [1] 315740e1-3591-0e11-923a-718e06c36445@arm.com