linux-kernel - Re: [PATCH v3 0/2] irqchip/gic-v3-its: Balance LPI affinity across CPUs

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Date:   Fri, 27 Mar 2020 17:47:08 +0000
From:   John Garry <john.garry@...wei.com>
To:     Marc Zyngier <maz@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     Jason Cooper <jason@...edaemon.net>,
        chenxiang <chenxiang66@...ilicon.com>,
        Robin Murphy <robin.murphy@....com>,
        "luojiaxing@...wei.com" <luojiaxing@...wei.com>,
        Ming Lei <ming.lei@...hat.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 0/2] irqchip/gic-v3-its: Balance LPI affinity across
 CPUs

> Before: ~1.2M IOPs fio read
> After: ~1.2M IOPs fio read
> 
> So they were about the same. I would have hoped for an improvement here, 
> considering before we would have all the per-queue threaded handlers 
> running on the single CPU handling the hard irq.
> 
> But we will retest all this tomorrow, so please consider these 
> provisional for now.
> 
> Thanks to Luo Jiaxing for testing.

Hi Marc,

Just to let you know that we're still looking at this. It turns out that 
we're not getting the results as hoped, and the previous results were 
incorrect due to a test booboo ..

I also think that the SMMU may even be creating a performance ceiling. I 
need to check this more, as I can't seem to get the throughput above a 
certain level.

I realise that we're so late in the cycle that there is now no immediate 
rush.

But I would also like to report some other unexpected behaviour for 
managed interrupts in this series - I'll reply directly to the specific 
patch for that.

Much appreciated,
John