linux-kernel - Re: [PATCH] IPI performance benchmark

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Date:   Wed, 13 Dec 2017 10:54:56 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ashish Kalra <Ashish.Kalra@...ium.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linu Cherian <Linu.Cherian@...ium.com>,
        Sunil Goutham <Sunil.Goutham@...ium.com>
Subject: Re: [PATCH] IPI performance benchmark

On Wed, Dec 13, 2017 at 01:47:47PM +0300, Yury Norov wrote:
> On Mon, Dec 11, 2017 at 10:33:32AM -0500, Konrad Rzeszutek Wilk wrote:
> > On Mon, Dec 11, 2017 at 05:16:00PM +0300, Yury Norov wrote:
> > > This benchmark sends many IPIs in different modes and measures
> > > time for IPI delivery (first column), and total time, ie including
> > > time to acknowledge the receive by sender (second column).
> > > 
> > > The scenarios are:
> > > Dry-run:	do everything except actually sending IPI. Useful
> > > 		to estimate system overhead.
> > > Self-IPI:	Send IPI to self CPU.
> > > Normal IPI:	Send IPI to some other CPU.
> > > Broadcast IPI:	Send broadcast IPI to all online CPUs.
> > > 
> > > For virtualized guests, sending and reveiving IPIs causes guest exit.
> > > I used this test to measure performance impact on KVM subsystem of
> > > Christoffer Dall's series "Optimize KVM/ARM for VHE systems".
> > > 
> > > https://www.spinics.net/lists/kvm/msg156755.html
> > > 
> > > Test machine is ThunderX2, 112 online CPUs. Below the results normalized
> > > to host dry-run time. Smaller - better.
> > 
> > Would it make sense to also add spinlock contention tests? Meaning make
> > this framework a bit more generic so you could do IPI and you could
> > also do spinlock contention?
> > 
> > Like:
> > http://xenbits.xen.org/gitweb/?p=xentesttools/bootstrap.git;a=blob;f=root_image/drivers/spinlock_hog/spinlock_hog.c;h=040a154808452576b1aa5720a6282981319a5360;hb=HEAD
> 
> There's kernel/locking/locktorture.c for spinlock testing. Maybe it
> worth to add new testcase there? If you find my 'framework' more
> suitable for you, I'm also OK with it. Is my understanding correct
> that you want something like broadcast IPI case, but with different
> payload?

Yes, exactly!

But as I said, you have probably other things on your mind so this
is more of - 'it would be cool if you could do it, but if you don't
get to it - I understand' type.