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

From: Arnd Bergmann <arnd@arndb.de>
To: Allen Pais <apais@linux.microsoft.com>
Cc: "Vinod Koul" <vkoul@kernel.org>, "Arnd Bergmann" <arnd@arndb.de>,
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Subject: Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue
Date: Tue, 31 May 2022 20:02:13 +0200	[thread overview]
Message-ID: <CAK8P3a3vf_huJ5ysBvFDV=11E-=OxFGiDQ9ND04YKug8g6jV_A@mail.gmail.com> (raw)
In-Reply-To: <0A9EDEDC-9E6C-47F8-89C0-48DCDD3F9DE3@linux.microsoft.com>

On Tue, May 31, 2022 at 7:02 PM Allen Pais <apais@linux.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