linux-kernel - Re: [PATCH] add rb_next in block throttle

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Message-ID: <20101201144234.GD4672@redhat.com>
Date:	Wed, 1 Dec 2010 09:42:35 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] add rb_next in block throttle

On Wed, Dec 01, 2010 at 09:11:01PM +0800, Hillf Danton wrote:
> On Tue, Nov 30, 2010 at 10:36 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> > On Fri, Nov 26, 2010 at 10:06:27PM +0800, Hillf Danton wrote:
> >> When selecting group for dispatching, the first entry of the service
> >> tree is sequentially dequeued, then the first entry is recomputed by
> >> calling rb_first().
> >>
> >> When the first is removed from service tree, new first could also be
> >> computed with rb_next(), since it could be faster than rb_first in
> >> this special environment.
> >>
> >> Signed-off-by: Hillf Danton <dhillf@...il.com>
> >> ---
> >
> > Ok. So set the leftmost element with the help of rb_next() at the time of
> > deletion of existing leftmost element. Not sure whether it is cheaper or
> > not but does not harm doing it this way.
> >
> > Have you tested it to make sure nothing is broken?
> 
> Hm..if broken, we rush out and gnarl at Andrea Arcangeli as loud as we could.
> 

Well, some testing is always good. This looks simple enough though.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Vivek

> Thanks
> Hillf
> >
> > Thanks
> > Vivek
> >
> >>
> >> --- a/block/blk-throttle.c    2010-11-01 19:54:12.000000000 +0800
> >> +++ b/block/blk-throttle.c    2010-11-26 21:27:40.000000000 +0800
> >> @@ -251,7 +251,7 @@ static void rb_erase_init(struct rb_node
> >>  static void throtl_rb_erase(struct rb_node *n, struct throtl_rb_root *root)
> >>  {
> >>       if (root->left == n)
> >> -             root->left = NULL;
> >> +             root->left = rb_next(n);
> >>       rb_erase_init(n, &root->rb);
> >>       --root->count;
> >>  }
> >> --
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