linux-hardening - Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue

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Message-ID: <CAK8P3a3vf_huJ5ysBvFDV=11E-=OxFGiDQ9ND04YKug8g6jV_A@mail.gmail.com>
Date:   Tue, 31 May 2022 20:02:13 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Allen Pais <apais@...ux.microsoft.com>
Cc:     Vinod Koul <vkoul@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        olivier.dautricourt@...lia.com, Stefan Roese <sr@...x.de>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
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        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
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        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
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        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        green.wan@...ive.com, Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Lyra Zhang <zhang.lyra@...il.com>,
        Patrice CHOTARD <patrice.chotard@...s.st.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Škrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        dmaengine@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue

On Tue, May 31, 2022 at 7:02 PM Allen Pais <apais@...ux.microsoft.com> wrote:

[note: something is wrong with your email client, your previous reply appears to
be in HTML]

> > That is a good idea, lot of drivers are waiting for completion which can
> > be signalled from hardirq, this would also reduce the hops we have and
> > help improve latency a bit. On the downside, some controllers provide
> > error information, which would need to be dealt with.
>
>
>    I am not an expert in dma subsystem, but by using completion from
> Hardirq context be a concern? Especially with latency.

I don't see how: to the task waiting for the completion, there should
be no difference, and for the irq handler sending it, it just avoids
a few cycles going into softirq context.

> > Yes that would be a very reasonable mechanism, thanks for the
> > suggestions.
>
>   I have started working on the idea of global softirq. A RFC should be ready
> For review soon.

Ok, thanks!

       Arnd