Re: [PATCH RESEND v9 2/3] fuse: add optional kernel-enforced timeout for requests

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Cc-ing Tomasz

On (24/11/28 11:23), Bernd Schubert wrote:
> > Thanks for the pointers again, Bernd.
> > 
> >> Miklos had asked for to abort the connection in v4
> >> https://lore.kernel.org/all/CAJfpegsiRNnJx7OAoH58XRq3zujrcXx94S2JACFdgJJ_b8FdHw@mail.gmail.com/raw
> > 
> > OK, sounds reasonable. I'll try to give the series some testing in the
> > coming days.
> > 
> > // I still would probably prefer "seconds" timeout granularity.
> > // Unless this also has been discussed already and Bernd has a link ;)
> 
> 
> The issue is that is currently iterating through 256 hash lists + 
> pending + bg.
> 
> https://lore.kernel.org/all/CAJnrk1b7bfAWWq_pFP=4XH3ddc_9GtAM2mE7EgWnx2Od+UUUjQ@mail.gmail.com/raw

Oh, I see.

> Personally I would prefer a second list to avoid the check spike and latency
> https://lore.kernel.org/linux-fsdevel/9ba4eaf4-b9f0-483f-90e5-9512aded419e@fastmail.fm/raw

That's good to know.  I like the idea of less CPU usage in general,
our devices a battery powered so everything counts, to some extent.

> What is your opinion about that? I guess android and chromium have an
> interest low latencies and avoiding cpu spikes?

Good question.

Can't speak for android, in chromeos we probably will keep it at 1 minute,
but this is because our DEFAULT_HUNG_TASK_TIMEOUT is larger than that (we
use default value of 120 sec). There are setups that might use lower
values, or even re-define default value, e.g.:

arch/arc/configs/axs101_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/arc/configs/axs103_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/arc/configs/axs103_smp_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/arc/configs/hsdk_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/arc/configs/vdk_hs38_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/arc/configs/vdk_hs38_smp_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=10
arch/powerpc/configs/mvme5100_defconfig:CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=20

In those cases 1 minute fuse timeout will overshot HUNG_TASK_TIMEOUT
and then the question is whether HUNG_TASK_PANIC is set.

On the other hand, setups that set much lower timeout than
DEFAULT_HUNG_TASK_TIMEOUT=120 will have extra CPU activities regardless,
just because watchdogs will run more often.

Tomasz, any opinions?