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From:   Thomas Gleixner <tglx@linutronix.de>
To:     xuyihang <xuyihang@huawei.com>, Ming Lei <ming.lei@redhat.com>
Cc:     Peter Xu <peterx@redhat.com>, Christoph Hellwig <hch@lst.de>,
        Jason Wang <jasowang@redhat.com>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>, minlei@redhat.com,
        liaochang1@huawei.com
Subject: Re: Virtio-scsi multiqueue irq affinity
In-Reply-To: <963e38b0-a7d6-0b13-af89-81b03028d1ae@huawei.com>
References: <20190318062150.GC6654@xz-x1> <alpine.DEB.2.21.1903231805310.1798@nanos.tec.linutronix.de> <20190325050213.GH9149@xz-x1> <20190325070616.GA9642@ming.t460p> <alpine.DEB.2.21.1903250948490.1798@nanos.tec.linutronix.de> <20190325095011.GA23225@ming.t460p> <0f6c8a5f-ad33-1199-f313-53fe9187a672@huawei.com> <87zgx5l8ck.ffs@nanos.tec.linutronix.de> <963e38b0-a7d6-0b13-af89-81b03028d1ae@huawei.com>
Date:   Mon, 10 May 2021 21:56:48 +0200
Message-ID: <87wns6gy67.ffs@nanos.tec.linutronix.de>
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Yihang,

On Mon, May 10 2021 at 16:48, xuyihang wrote:
> =E5=9C=A8 2021/5/8 20:26, Thomas Gleixner =E5=86=99=E9=81=93:
>> Can you please provide a more detailed description of your system?

>>      - Kernel version
> This experiment run on linux-4.19

Again. Please provide reports against the most recent mainline version
and not against some randomly picked kernel variant.

> If we make some change on this experiment:
>
> 1.=C2=A0 Make this RT application use less CPU time instead of 100%, the =
problem
> disappear.
>
> 2, If we change rq_affinity to 2, in order to avoid handle softirq on=20
> the same core of RT thread, the problem also disappear. However, this app=
roach
> result in about 10%-30% random write proformance deduction comparing
> to rq_affinity =3D 1, since it may has better cache utilization.
> echo 2 > /sys/block/sda/queue/rq_affinity
>
> Therefore, I want to exclude some CPU from managed irq on boot
> parameter,

Why has this realtime thread to run on CPU0 and cannot move to some
other CPU?

> which has simliar approach to 11ea68f553e2 ("genirq, sched/isolation:=20
> Isolate from handling managed interrupts").

Why can't you use the existing isolation mechanisms?

Thanks,

        tglx