linux-kernel - Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support

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Message-ID: <87bmmyedb5.fsf@firstfloor.org>
Date:   Tue, 29 Aug 2017 06:03:26 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Yang Zhang <yang.zhang.wz@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        wanpeng.li@...mail.com, mst@...hat.com, pbonzini@...hat.com,
        tglx@...utronix.de, rkrcmar@...hat.com, dmatlack@...gle.com,
        agraf@...e.de, peterz@...radead.org, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support

Yang Zhang <yang.zhang.wz@...il.com> writes:

> Some latency-intensive workload will see obviously performance 
> drop when running inside VM. The main reason is that the overhead 
> is amplified when running inside VM. The most cost i have seen is 
> inside idle path. 

You could test with https://lkml.org/lkml/2017/7/9/204
which optimizes these idle paths with a fast path.

If that works it would be a far better solution than
explicit tunables and basically giving up by polling.

-Andi