Messages in this thread | | | Date | Wed, 31 Aug 2022 12:27:12 -0400 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH] random: use raw spinlocks for use on RT |
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On Tue, Aug 30, 2022 at 08:57:47PM +0200, Sebastian Andrzej Siewior wrote: > On 2022-08-30 11:24:33 [-0400], Jason A. Donenfeld wrote: > > Hi Sebastian, > Hi Jason, > > > On Tue, Aug 30, 2022 at 12:13:44PM +0200, Sebastian Andrzej Siewior wrote: > > > The first patch did so yes. The second simply retried in two secs and > > > this shouldn't be problematic. > > > > This seemed pretty bad too, because now you potentially miss up to 2 > > seconds of messages AND it adds more complexity. > > It is early at boot and it could be reduced to one if it helps. I > remember you had a suggestion where we would lose always the first print > out on RT you said it is okay since you can't rely on that…
I mean, the mechanism now is simple and doesn't fail. What you're suggesting is more complex and fails sometimes. So,
> > I'm fine with changing things up to accommodate RT, but not when the > > result is so obviously worse than before. > > I don't think it is worse. This is your opinion and I did not hear any > other feedback so far.
so, I think it's beyond a matter of opinion and is actually objectively worse.
And it's not like I even care particularly much about vnsprintf; as I said before, none of this really matters _that_ much. But I *do* very much object to dirtying up random bits of code and making things actually worse in the name of RT, especially when there are other solutions being considered. Namely:
> > In my tests I can't see any latency difference with using raw spinlocks > > in random.c. Maybe I'm doing things wrong? But I'm not seeing anything > > change... > > You need to look at the maximum latency that may happen. Also the other > thing is that there is no need to add raw_spinlock_t locking if it can > be avoided.
I really am having trouble fashioning a test that shows a higher maximum latency. All the RNG critical sections are really short in the end. So I dunno... seems like not a big deal to me. If you're seeing different numbers, can you post them and how you came up with them? If I can reproduce it, maybe it's possible for me to do something about that latency. But so far I'm not seeing any latency spike...
Jason
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