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

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Message-ID: <AANLkTimAAr7PgH85G+yqOXwdExRUHbZm3HXz0WsRjLuW@mail.gmail.com>
Date:	Wed, 1 Dec 2010 21:11:01 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] add rb_next in block throttle

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.

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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