Re: [PATCH] rtase: Avoid sleeping in get_stats64()

[Alexander Lobakin]

From: David Laight <david.laight.linux@xxxxxxxxx>
Date: Mon, 1 Jun 2026 22:42:03 +0100

> On Mon, 1 Jun 2026 15:14:50 +0200
> Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> wrote:
> 
>> From: Justin Lai <justinlai0215@xxxxxxxxxxx>
>> Date: Mon, 1 Jun 2026 14:24:47 +0800
>>
>>> The .ndo_get_stats64 callback must not sleep because it can be
>>> called when reading /proc/net/dev.
>>>
>>> rtase_get_stats64() calls rtase_dump_tally_counter(), which polls
>>> the tally counter dump bit with read_poll_timeout(). This may
>>> sleep while waiting for the hardware counter dump to complete.
>>>
>>> Use read_poll_timeout_atomic() instead to avoid sleeping in the
>>> get_stats64() path.
>>>
>>> Signed-off-by: Justin Lai <justinlai0215@xxxxxxxxxxx>  
>>
>> Looks legit.
>>
>> One question: for how long can this poll for in real life scenarios? Up
>> to ~1 ms is okay-ish for atomic, but if longer, then you'd better to
>> split it into shorter polls and reschedule() time to time.
> 
> Anyone trying to get a thread running at an RT priority won't thank you
> for spinning for anywhere near that long.
> When an RT processes becomes runnable the scheduler will preempt a lower
> priority process that is running on the cpu the RT process last ran on.
> The RT process won't run until the preempt actually happens.
> 
> 1ms is a very long time.

That's why I wrote "okay-ish". Ideally atomic polling should not go past
100 us, I usually used it for no longer than 10-50 us.

The author says that it usually takes around 25 us which is acceptable
I'd say.

Thanks,
Olek