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Re: [Qemu-devel] [RFC PATCH 6/8] quorum: Avoid bdrv_aio_writev() for rew

From: Alberto Garcia
Subject: Re: [Qemu-devel] [RFC PATCH 6/8] quorum: Avoid bdrv_aio_writev() for rewrites
Date: Fri, 18 Nov 2016 13:33:52 +0100
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Fri 18 Nov 2016 01:21:12 PM CET, Kevin Wolf wrote:
>> > +    /* one less rewrite to do */
>> > +    acb->rewrite_count--;
>> > +    qemu_coroutine_enter_if_inactive(acb->co);
>> I think you should only enter acb->co when acb->rewrite_count reaches
>> zero.
>> In all other cases the main coroutine simply iterates inside the
>> while() loop, verifies that the number is still positive and yields
>> again.
>> The same applies to all other cases of
>> qemu_coroutine_enter_if_inactive, by the way (I failed to notice it
>> in patch #5).
> I think I like it better this way because it keeps the loop condition
> local to the caller instead of spreading it across the caller and the
> places that reenter. On the other hand, I can see that not doing the
> extra context switch might be a little more efficient.

Apart from the efficiency, I actually find it a bit easier to understand
if it's made explicit:

    /* Once all rewrites are done we can wake up the caller */
    if (--acb->rewrite_count == 0) {

But I can understand that some people may find your way easier. I don't
feel strongly about it, so no need to change it.


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