Re: [Xen-devel] Fwd: xen: credit2: credit2 can’t reach the throughput as expected

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Mon, 2019-02-18 at 14:04 +0000, zheng chuan wrote:
> Hi, Dario
>
Hi,

> [sorry for the html email format, resend by text.]
> 
Thanks! :-)

> > On Fri, 2019-02-15 at 06:15 +0000, zheng chuan wrote:
> > > 
> > Now, can I ask you a favour? Can you rerun with:
> > 
> > sched_credit2_migrate_resist=0
> > 
> > added to Xen's boot command line?
> > 
> Unfortunately, sched_credit2_migrate_resist=0 seems do not work :(
> It still around 60% and 120% for guest_1 and guest_2 with
> ratelimiting of 1ms, respectively
> 
Ok, I was just curios. Thanks for doing the test.

> > But can we actually try to measure latency as well? Because it
> > looks to me that
> > we're discussing while having only half of the picture available.
> > 
> Sure, but due to my lack of knowledge, does xen have sched_latency
> measurement
> tools like perf sched_latency for CFS ? I will give it try to do it
> if I get it.
> 
No, we don't have anything like that. When speaking of measuring
latencies, I was mainly thinking to logging some timestamps from your
app.

Anyway, I just wanted to let you know that I'm looking into this, but
it's a few days that I don't feel very well, that's why I wasn't
replying to emails.

I'll get back to it when I'm better.

> What I am tried is rude and empirical, which is shown as bellow:
> 
> diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
> index 9a3e71f..b781ebe 100644
> --- a/xen/common/sched_credit2.c
> +++ b/xen/common/sched_credit2.c
> @@ -1642,13 +1642,13 @@ static void reset_credit(const struct
> scheduler *ops, int cpu, s_time_t now,
> if ( snext->credit < -CSCHED2_CREDIT_INIT )
> m += (-snext->credit) / CSCHED2_CREDIT_INIT;
> 
> - list_for_each( iter, &rqd->svc )
> + list_for_each( iter, &rqd->runq )
> {
>
Ok, I see. Well, if we do something like this, we'll have to figure out
what happens when one of the vcpu which didn't get the credit reset,
wakes up, and how that influence the algorithm.

I was thinking more to have csched2_runtime() return something
"clever", but I have no precise idea yet.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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