linux-kernel - Re: [PATCH v2 00/59] KVM: iommu: Overhaul device posted IRQs support

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Message-ID: <aEbw2zBUQwJZ3D98@google.com>
Date: Mon, 9 Jun 2025 07:34:03 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sairaj Kodilkar <sarunkod@....com>
Cc: baolu.lu@...ux.intel.com, dmatlack@...gle.com, dwmw2@...radead.org, 
	francescolavra.fl@...il.com, iommu@...ts.linux.dev, joao.m.martins@...cle.com, 
	joro@...tes.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	mlevitsk@...hat.com, pbonzini@...hat.com, vasant.hegde@....com
Subject: Re: [PATCH v2 00/59] KVM: iommu: Overhaul device posted IRQs support

On Mon, Jun 09, 2025, Sairaj Kodilkar wrote:
> Hi Sean,
> 
> Sorry for the delay in testing. All sanity tests are OK. I reran the performance 
> test on the V2 and noticed that V2 has significantly more GALOG entries than V1
> for all three cases. I also noticed that the Guest Nvme interrupt rate has
> dropped for the 192 VCPUS.

Hmm, I don't see any obvious bugs or differences (based on a code diffed between
v1 and v2).  I'll poke at the GALogIntr behavior just to double check, but my
guess is that the differences are due to exernal factors, e.g. guest behavior,
timing, scheduling, etc.

IOPS are all nearly identical, so I'm not terribly concerned.
 
> I haven't figured out what is causing this.

Might just be slight differences in guest behavior?  E.g. did you change the guest
kernel?  

> I will continue my investigation further.
> 
>                           VCPUS = 32, Jobs per NVME = 8
> ==============================================================================================
>                                          V2                         V1          Percent change
> ----------------------------------------------------------------------------------------------
> Guest Nvme interrupts               124,260,796                 124,559,110             -0.20%
> IOPS (in kilo)                            4,790                       4,796             -0.01%

Uber nit, the percent change should be -0.10%

> GALOG entries                              8117                         169              4702%
> ----------------------------------------------------------------------------------------------
> 
> 
>                           VCPUS = 64, Jobs per NVME = 16
> ==============================================================================================
>                                          V2                         V1          Percent change
> ----------------------------------------------------------------------------------------------
> Guest Nvme interrupts              102,394,358                   99,800,056             2.00% 
> IOPS (in kilo)                           4,796                        4,798            -0.04% 
> GALOG entries                           19,057                       11,923            59.83%
> ----------------------------------------------------------------------------------------------
> 
> 
>                          VCPUS = 192, Jobs per NVME = 48
> ==============================================================================================
>                                          V2                         V1          Percent change
> ----------------------------------------------------------------------------------------------
> Guest Nvme interrupts               68,363,232                  78,066,512             -12.42%
> IOPS (in kilo)                           4,751                       4,749              -0.04%

Uber nit #2, percent change should be postive 0.04%?  4,751 > 4,749.

> GALOG entries                           62,768                      56,215              11.66%
> ----------------------------------------------------------------------------------------------
> 
> Thanks
> Sairaj