linux-kernel - Re: [PATCH 06/18] compat: backport ASYNC_DOMAIN

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Message-ID: <CAB=NE6VKT11k95Szi4NmigKCgMJ1XJoU3+rACbJpnWwUpCC1EA@mail.gmail.com>
Date:	Wed, 10 Apr 2013 12:19:40 -0700
From:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	"backports@...r.kernel.org" <backports@...r.kernel.org>,
	Dan Williams <dcbw@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/18] compat: backport ASYNC_DOMAIN_EXCLUSIVE()

On Wed, Apr 10, 2013 at 11:20 AM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Wed, 2013-04-10 at 10:26 -0700, Luis R. Rodriguez wrote:
>
>> > I guess I'd have to review the async API,
>>
>> Yeap, reviewing the commit noted would help too.
>
> Yeah ... :)
>
>> > What's the use of just this when you don't have things like
>> > async_schedule_domain() and async_synchronize_full_domain(), regulator
>> > stuff wouldn't compile I think?
>>
>> You mean is not having the full asynch that deals with all registered
>> domains likely to have an issue on the useres of
>> async_synchronize_full_domain() ? Lets better ask Dan.
>
> I don't know. However it seems that in order to have an ASYNC_DOMAIN()
> or ASYNC_DOMAIN_EXCLUSIVE() you always need to *do* something with it,
> so for that you'd also need the functions async_schedule_domain() and
> async_synchronize_full_domain() or similar, at least, no?
>
> The point here seems to be making boot faster by starting a bunch of
> async probing inside a domain, and then you wait for the entire domain,
> so everything that's in that domain can be done in parallel.
>
> Say for example you have 20 SCSI drives. If you look at them serially
> then you'd waste much time waiting for the drives. The point here
> appears to be that you create a domain (using this macro), then add all
> the drives to the domain and then wait for the domain to finish.
>
> However, it seems entirely pointless to backport just a small part of
> the API?

Oh I agree don't get me wrong, however porting kernel/async.c seems
like a rather separate effort worth considering. As-is though I have
not seen any negative impact though to keep older subsystems from
compiling, ie its a no-op for older kernels as I see it.

 Luis
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