linux-kernel - Re: [PATCH] RFC: abstract access to xtime

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Message-ID: <AANLkTikS0WAUngUXVx3uCynXt07-1L+=aR5A09XOMtK9@mail.gmail.com>
Date:	Thu, 20 Jan 2011 11:37:19 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Torben Hohn <torbenh@....de>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...x.de>
Subject: Re: [PATCH] RFC: abstract access to xtime_lock into a set of inline functions

On Thu, Jan 20, 2011 at 9:30 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Thu, Jan 20, 2011 at 06:14:08PM +0100, Torben Hohn wrote:
>> the -rt patches change the xtime_lock to a raw_seqlock_t
>> so a pretty huge portion of the patch deals with changing
>> the locking functions.
>>
>> this commit uses inline functions, to hide the type
>> of the lock.
>
> That's not how kernel code usually works.

Yea, I'm not a fan of this patch either.


>> -     write_seqlock(&xtime_lock);
>> +     xtime_write_seqlock();
>>       do_timer(1);
>> -     write_sequnlock(&xtime_lock);
>> +     xtime_write_sequnlock();
>
> However there's a pretty clear pattern of taking xtime_lock, calling
> do_timer and then releasing.  A useful thing you could do is to rename
> do_timer to do_timer_locked and make do_timer take and release
> xtime_lock in one place.

Seems like a reasonable suggestion.  I suspect there's still quite a
bit of stuff done under the same lock right around do_timer on a
number of arches, but  having a locked call would cut down on how
widely xtime is used.

thanks
-john
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