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

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 04/15] coroutine: add a knob to disable the shared release pool
Date: Tue, 28 Jun 2016 12:41:06 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

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...


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