linux-kernel - Re: [PATCH v2 RESEND] io_uring/fdinfo: add timeout

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Message-ID: <e8d1f8e8-abd9-4e4b-aa55-d8444794f55a@gmail.com>
Date: Thu, 10 Oct 2024 16:35:59 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Ruyi Zhang <ruyi.zhang@...sung.com>, axboe@...nel.dk
Cc: io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
 peiwei.li@...sung.com
Subject: Re: [PATCH v2 RESEND] io_uring/fdinfo: add timeout_list to fdinfo

On 10/10/24 10:20, Ruyi Zhang wrote:
> ---
> On 25 Sep 2024 12:58 Pavel Begunkov wrote
>> On 9/25/24 09:58, Ruyi Zhang wrote:
>>> io_uring fdinfo contains most of the runtime information,which is
>>> helpful for debugging io_uring applications; However, there is
>>> currently a lack of timeout-related information, and this patch adds
>>> timeout_list information.
> 
>> Please refer to unaddressed comments from v1. We can't have irqs
>> disabled for that long. And it's too verbose (i.e. depends on
>> the number of timeouts).
> 
> Two questions:
> 
> 1. I agree with you, we shouldn't walk a potentially very long list
> under spinlock. but i can't find any other way to get all the timeout

If only it's just under the spin, but with disabled irqs...

> information than to walk the timeout_list. Do you have any good ideas?

In the long run it'd be great to replace the spinlock
with a mutex, i.e. just ->uring_lock, but that would might be
a bit involving as need to move handling to the task context.

> 2. I also agree seq_printf heavier, if we use seq_put_decimal_ull and
> seq_puts to concatenate strings, I haven't tested whether it's more
> efficient or not, but the code is certainly not as readable as the
> former. It's also possible that I don't fully understand what you mean
> and want to hear your opinion.

I don't think there is any difference, it'd be a matter of
doubling the number of in flight timeouts to achieve same
timings. Tell me, do you really have a good case where you
need that (pretty verbose)? Why not drgn / bpftrace it out
of the kernel instead?

-- 
Pavel Begunkov