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

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Message-ID: <d76452b5-fd30-f418-ff4f-de10dfa831a7@redhat.com>
Date:   Tue, 21 Sep 2021 19:50:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Suleiman Souhlal <suleiman@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: do not shrink halt_poll_ns below grow_start

On 15/09/21 03:42, Sergey Senozhatsky wrote:
> 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
> 

Queued, thanks.

Paolo