linux-kernel - Re: [PATCH] KVM: arm64: Limit stage2_apply

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Date: Thu, 4 Apr 2024 14:41:56 -0700
From: Krister Johansen <kjlx@...pleofstupid.com>
To: Ali Saidi <alisaidi@...zon.com>
Cc: catalin.marinas@....com, james.morse@....com, kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	maz@...nel.org, me@...idreaver.com, oliver.upton@...ux.dev,
	suzuki.poulose@....com, will@...nel.org, yuzenghui@...wei.com
Subject: Re: [PATCH] KVM: arm64: Limit stage2_apply_range() batch size to
 smallest block

On Thu, Apr 04, 2024 at 09:27:42PM +0000, Ali Saidi wrote:
> > Just a quick followup that I did test Will's patches and didn't find
> > that it changed the performance of the workload that I'd been testing.
> > IOW, I wasn't able to discern a network performance difference between
> > the baseline and those changes.
> 
> That is a bit unexpected that the performance wasn't worse with the patch Will
> sent because it should have disabled the range invalidates since they these 
> invalidates will be getting rid of blocks?  Which Graviton were you testing
> this on? 

Sorry I didn't mention it earlier.  This was on a Graviton 4 with
FEAT_TLBIRANGE.  Due to the placement of the test machine and the client
the max single flow rate was 5Gbps, and with both the baseline and
Will's patches I wasn't able to discern any slowdown there, at least in
terms of impact to the adjacent networking traffic.  I saw an approx 1%
slowdown with multiple flows at 10Gbps, but didn't have a baseline for
that test case so was hesitant to offer it as conclusive.  I should be
clear that I _wasn't_ measuring the the teardown times in this test
-- just how the teardown itself impacted the networking performance.

-K