Re: [Qemu-devel] [PATCH 04/15] coroutine: add a knob to disable the shared release pool

[Peter Lieven <pl@kamp.de>]

Am 28.06.2016 um 12:41 schrieb Paolo Bonzini:
>
> On 28/06/2016 11:01, Peter Lieven wrote:
>> the current coroutine freelist implementation has 2 kinds of pools.
>> One shared release pool between all threads and additionally one
>> allocation pool per thread. The release pool is especially necessary
>> if the coroutine is created in a different thread than it is released.
>> This is e.g. the case if an IDE interface is used.
>>
>> But in times of virtio and dataplane the the release pool adds costs
>> which are not entirely necessary. At first if virtio is used the release
>> pool tends to fill up to 100% because all coroutines are first handed
>> back to the release pool. On coroutine create a thread can steal this
>> release pool and make it its local allocation pool, but during mixed
>> I/O pattern at the end the release pool is full of useless coroutines
>> and the alloc_pool has also filled to maximum size.
> The cost is 2^16 bytes * 2^6 coroutines, that is 4 MB.  I don't think
> this is worth an extra knob that no one will use...

You are right, I was having this patch prior to reducing the stack size.
In fact its 2 * 2^6 coroutines. But maybe its worth of thinking making
the release_pool the same max size as the alloc_pool? Otherwise when
the release_pool is stolen it could make the alloc_pool also that big.

Peter