From: Paolo Bonzini <pbonzini@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>, Radim Krcmar <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org, Luiz Capitulino <lcapitulino@redhat.com>,
Rik van Riel <riel@redhat.com>
Subject: Re: [patch 2/3] KVM: x86: add option to advance tscdeadline hrtimer expiration
Date: Wed, 17 Dec 2014 18:48:26 +0100 [thread overview]
Message-ID: <5491C1EA.7040706@redhat.com> (raw)
In-Reply-To: <20141217174139.GA31721@amt.cnet>
On 17/12/2014 18:41, Marcelo Tosatti wrote:
>> > Btw. simple automatic delta tuning had worse results?
> Haven't tried automatic tuning.
>
> So what happens on a realtime environment is this: you execute the fixed
> number of instructions from interrupt handling all the way to VM-entry.
>
> Well, almost fixed. Fixed is the number of apic_timer_fn plus KVM
> instructions. You can also execute host scheduler and timekeeping
> processing.
>
> In practice, the length to execute that instruction sequence is a bell
> shaped normal distribution around the average (the right side is
> slightly higher due to host scheduler and timekeeping processing).
>
> You want to advance the timer by the rightmost bucket, that way you
> guarantee lower possible latencies (which is the interest here).
>
> That said, i don't see advantage in automatic tuning for the usecase
> which this targets.
Yeah, the value of the parameter can be computed pretty easily from
either the tracepoint or the kvm-unit-tests testcase.
Paolo
next prev parent reply other threads:[~2014-12-17 17:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-16 14:08 [patch 0/3] KVM: add option to advance tscdeadline hrtimer expiration (v5) Marcelo Tosatti
2014-12-16 14:08 ` [patch 1/3] KVM: x86: add method to test PIR bitmap vector Marcelo Tosatti
2014-12-17 14:45 ` Radim Krcmar
2014-12-16 14:08 ` [patch 2/3] KVM: x86: add option to advance tscdeadline hrtimer expiration Marcelo Tosatti
2014-12-17 14:58 ` Radim Krcmar
2014-12-17 17:41 ` Marcelo Tosatti
2014-12-17 17:48 ` Paolo Bonzini [this message]
2014-12-17 19:36 ` Radim Krcmar
2014-12-18 12:24 ` Marcelo Tosatti
2014-12-23 13:18 ` Paolo Bonzini
2014-12-16 14:08 ` [patch 3/3] KVM: x86: add tracepoint to wait_lapic_expire Marcelo Tosatti
2014-12-17 15:06 ` Radim Krcmar
-- strict thread matches above, loose matches on Subject: below --
2014-12-23 20:58 [patch 0/3] KVM: add option to advance tscdeadline hrtimer expiration (v6) Marcelo Tosatti
2014-12-23 20:58 ` [patch 2/3] KVM: x86: add option to advance tscdeadline hrtimer expiration Marcelo Tosatti
2015-01-05 18:12 ` Radim Krcmar
2015-01-05 18:20 ` Radim Krcmar
2015-01-08 17:41 ` Marcelo Tosatti
2015-01-08 21:44 ` Paolo Bonzini
2014-12-15 22:06 [patch 0/3] KVM: add option to advance tscdeadline hrtimer expiration (v4) Marcelo Tosatti
2014-12-15 22:06 ` [patch 2/3] KVM: x86: add option to advance tscdeadline hrtimer expiration Marcelo Tosatti
2014-12-16 14:34 ` Paolo Bonzini
2014-12-16 15:13 ` Marcelo Tosatti
2014-12-16 15:18 ` Paolo Bonzini
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