linux-kernel - Re: [PATCH] KVM: do not shrink halt_poll_ns below grow

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Message-ID: <YUFPcphBWO8bz7Lk@google.com>
Date:   Wed, 15 Sep 2021 10:42:10 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Suleiman Souhlal <suleiman@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] KVM: do not shrink halt_poll_ns below grow_start

On (21/09/02 12:11), Sergey Senozhatsky wrote:
> grow_halt_poll_ns() ignores values between 0 and
> halt_poll_ns_grow_start (10000 by default). However,
> when we shrink halt_poll_ns we may fall way below
> halt_poll_ns_grow_start and endup with halt_poll_ns
> values that don't make a lot of sense: like 1 or 9,
> or 19.
> 
> VCPU1 trace (halt_poll_ns_shrink equals 2):
> 
> VCPU1 grow 10000
> VCPU1 shrink 5000
> VCPU1 shrink 2500
> VCPU1 shrink 1250
> VCPU1 shrink 625
> VCPU1 shrink 312
> VCPU1 shrink 156
> VCPU1 shrink 78
> VCPU1 shrink 39
> VCPU1 shrink 19
> VCPU1 shrink 9
> VCPU1 shrink 4
> 
> Mirror what grow_halt_poll_ns() does and set halt_poll_ns
> to 0 as soon as new shrink-ed halt_poll_ns value falls
> below halt_poll_ns_grow_start.

Gentle ping.

	-ss