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Date: Fri, 28 Nov 2014 09:13:55 +0100
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] [RFC PATCH 3/3] qemu-coroutine: use a ring per
 thread for the pool
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To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, famz@redhat.com, benoit@irqsave.net, ming.lei@canonical.com, armbru@redhat.com, mreitz@redhat.com, stefanha@redhat.com

Am 27.11.2014 um 17:40 schrieb Paolo Bonzini:
>
> On 27/11/2014 11:27, Peter Lieven wrote:
>> +static __thread struct CoRoutinePool {
>> +    Coroutine *ptrs[POOL_MAX_SIZE];
>> +    unsigned int size;
>> +    unsigned int nextfree;
>> +} CoPool;
>>  
> The per-thread ring unfortunately didn't work well last time it was
> tested.  Devices that do not use ioeventfd (not just the slow ones, even
> decently performing ones like ahci, nvme or megasas) will create the
> coroutine in the VCPU thread, and destroy it in the iothread.  The
> result is that coroutines cannot be reused.
>
> Can you check if this is still the case?

I already tested at least for IDE and for ioeventfd=off. The coroutine
is created in the vCPU thread and destroyed in the I/O thread.

I also havea more complicated version which sets per therad coroutine pool only
for dataplane. Avoiding the lock for dedicated iothreads.

For those who want to take a look:

https://github.com/plieven/qemu/commit/325bc4ef5c7039337fa785744b145e2bdbb7b62e

Peter