linux-kernel - Re: [RESPIN PATCH] irqchip/gic-v4.1: Use local 4

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Message-ID: <86a5j1ilqg.wl-maz@kernel.org>
Date: Mon, 01 Jul 2024 09:01:59 +0100
From: Marc Zyngier <maz@...nel.org>
To: Nianyao Tang <tangnianyao@...wei.com>
Cc: <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	<guoyang2@...wei.com>,
	<wangwudi@...ilicon.com>
Subject: Re: [RESPIN PATCH] irqchip/gic-v4.1: Use local 4_1 ITS to generate VSGI

Please don't use "RESPIN" as a subject tag. This means nothing, and
confuses the tooling such as b4, which expects a version number.

If the code has changed in any way, increment the version number. This
really should have been a v2.

On Mon, 01 Jul 2024 07:20:42 +0100,
Nianyao Tang <tangnianyao@...wei.com> wrote:
> 
> On multi-node GICv4.1 system, VSGI senders always use one certain 4_1 ITS,
> because find_4_1_its return the first its_node in list, regardless of
> which node the VSGI sender is on. This brings guest vsgi performance drop
> when VM is not deployed on the same node as this returned ITS.

s/deployed/running/

> 
> On a 2-socket environment, each with one ITS and 32 cpu, GICv4.1 enabled,
> 4U8G guest, 4 vcpu is deployed on same socket.

s/deployed/running/

> When VM on socket0, kvm-unit-tests ipi_hw result is 850ns.
> When VM on socket1, it is 750ns. The reason is VSGI sender always
> use lasted reported ITS(that on socket1) to inject VSGI. The access

s/lasted/the last/

> from cpu to other-socket ITS will cost 100ns more compared to cpu to 
> local ITS.
> 
> To use local ITS, we can get 12% reduction in IPI latency.

s/To use/By using a/

> 
> The patch modify find_4_1_its to firstly return per-cpu local_4_1_its,

Drop "the patch".

s/firstly/first/

> which is init when inherit the VPE table from the ITS on secondary CPUs.

or from another CPU.

> If fail to find local 4_1 ITS, return any 4_1 ITS like before.
> 
> Signed-off-by: Nianyao Tang <tangnianyao@...wei.com>
> Reviewed-by: Marc Zyngier <maz@...nel.org>

No. I never gave this tag. You can (and probably should) add a
"Suggested-by:" tag, but not a "Reviewed-by:", until I explicitly
reply to the patch with that tag.

Please resend it as a v3 with all of the above fixed.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.