Re: [PATCH v8 00/74] per-CPU locks

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/27/20 6:14 AM, Emilio G. Cota wrote:
> (Apologies if I missed some Cc's; I was not Cc'ed in patch 0
>   so I'm blindly crafting a reply.)
> 
> On Thu, Mar 26, 2020 at 15:30:43 -0400, Robert Foley wrote:
>> This is a continuation of the series created by Emilio Cota.
>> We are picking up this patch set with the goal to apply
>> any fixes or updates needed to get this accepted.
> 
> Thanks for picking this up!
> 
>> Listed below are the changes for this version of the patch,
>> aside from the merge related changes.
>>
>> Changes for V8:
>> - Fixed issue where in rr mode we could destroy the BQL twice.
> 
> I remember doing little to no testing in record-replay mode, so
> there should be more bugs hiding in there :-)
> 
>> - Found/fixed bug that had been hit in testing previously during
>> the last consideration of this patch.
>>   We reproduced the issue hit in the qtest: bios-tables-test.
>>   The issue was introduced by dropping the BQL, and found us
>>   (very rarely) missing the condition variable wakeup in
>>   qemu_tcg_rr_cpu_thread_fn().
> 
> Aah, this one:
>    https://patchwork.kernel.org/patch/10838149/#22516931
> How did you identify the problem? Was it code inspection or using a tool
> like rr? I remember this being hard to reproduce reliably.
> 
> On a related note, I've done some work to get QEMU-system to work
> under thread sanitizer, since tsan now supports our longjmp-based
> coroutines (hurrah!). My idea was to integrate tsan in QEMU (i.e.
> bring tsan warnings to 0) before (re)trying to merge the
> per-CPU lock patchset; this would minimize the potential for
> regressions, which from my personal viewpoint seems like a reasonable
> thing to do especially now that I have little time to work on QEMU.
> 
> If there's interest in doing the tsan work first, then I'd be
> happy to send to the list as soon as this weekend the changes that
> I have so far [1].

I'm pretty sure Marc-André is interested (and also Stefan maybe), so 
Cc'ing them.

> 
> Thanks,
> 		Emilio
> 
> [1] WIP branch: https://github.com/cota/qemu/commits/tsan
>