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From: Dave Hansen <dave@sr71.net>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	dave.jiang@intel.com, akpm@linux-foundation.org,
	dhillf@gmail.com, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH] mm: call cond_resched() per MAX_ORDER_NR_PAGES pages copy
Date: Mon, 18 Nov 2013 14:29:24 -0800	[thread overview]
Message-ID: <528A94C4.80101@sr71.net> (raw)
In-Reply-To: <1384811778-7euptzgp-mutt-n-horiguchi@ah.jp.nec.com>

On 11/18/2013 01:56 PM, Naoya Horiguchi wrote:
>> > Why bother trying to "optimize" it?
> I thought that if we call cond_resched() too often, the copying thread can
> take too long in a heavy load system, because the copying thread always
> yields the CPU in every loop.

I think you're confusing cond_resched() and yield().  The way I look at it:

yield() means: "Hey scheduler, go right now and run something else I'm
done running"

cond_resched() means: "Schedule me off if the scheduler has already
decided something else _should_ be running"

I'm sure I'm missing some of the subtleties, but as I see it, yield()
actively goes off and finds something else to run.  cond_resched() only
schedules you off if you've *already* run too long.


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WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave@sr71.net>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	dave.jiang@intel.com, akpm@linux-foundation.org,
	dhillf@gmail.com, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH] mm: call cond_resched() per MAX_ORDER_NR_PAGES pages copy
Date: Mon, 18 Nov 2013 14:29:24 -0800	[thread overview]
Message-ID: <528A94C4.80101@sr71.net> (raw)
In-Reply-To: <1384811778-7euptzgp-mutt-n-horiguchi@ah.jp.nec.com>

On 11/18/2013 01:56 PM, Naoya Horiguchi wrote:
>> > Why bother trying to "optimize" it?
> I thought that if we call cond_resched() too often, the copying thread can
> take too long in a heavy load system, because the copying thread always
> yields the CPU in every loop.

I think you're confusing cond_resched() and yield().  The way I look at it:

yield() means: "Hey scheduler, go right now and run something else I'm
done running"

cond_resched() means: "Schedule me off if the scheduler has already
decided something else _should_ be running"

I'm sure I'm missing some of the subtleties, but as I see it, yield()
actively goes off and finds something else to run.  cond_resched() only
schedules you off if you've *already* run too long.



  reply	other threads:[~2013-11-18 22:30 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-15 22:55 [v3][PATCH 0/2] v3: fix hugetlb vs. anon-thp copy page Dave Hansen
2013-11-15 22:55 ` Dave Hansen
2013-11-15 22:55 ` [v3][PATCH 1/2] mm: hugetlbfs: Add VM_BUG_ON()s to catch non-hugetlbfs pages Dave Hansen
2013-11-15 22:55   ` Dave Hansen
2013-11-15 22:55 ` [v3][PATCH 2/2] mm: thp: give transparent hugepage code a separate copy_page Dave Hansen
2013-11-15 22:55   ` Dave Hansen
2013-11-18 10:32   ` Mel Gorman
2013-11-18 10:32     ` Mel Gorman
2013-11-18 18:51   ` [v3][PATCH 2/2] mm: thp: give transparent hugepage code aseparate copy_page Naoya Horiguchi
2013-11-18 18:51     ` Naoya Horiguchi
2013-11-18 18:54     ` [PATCH] mm: call cond_resched() per MAX_ORDER_NR_PAGES pages copy Naoya Horiguchi
2013-11-18 18:54       ` Naoya Horiguchi
2013-11-18 19:02       ` Dave Hansen
2013-11-18 19:02         ` Dave Hansen
2013-11-18 20:20         ` Naoya Horiguchi
2013-11-18 20:20           ` Naoya Horiguchi
2013-11-18 20:48           ` Dave Hansen
2013-11-18 20:48             ` Dave Hansen
2013-11-18 21:56             ` Naoya Horiguchi
2013-11-18 21:56               ` Naoya Horiguchi
2013-11-18 22:29               ` Dave Hansen [this message]
2013-11-18 22:29                 ` Dave Hansen
2013-11-19  0:34                 ` Naoya Horiguchi
2013-11-19  0:34                   ` Naoya Horiguchi
2013-11-18 19:23 ` [v3][PATCH 0/2] v3: fix hugetlb vs. anon-thp copy page Jiang, Dave
2013-11-18 19:23   ` Jiang, Dave

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