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Date: Thu, 30 Jul 2015 09:58:03 -0700
From: =?iso-8859-1?Q?J=F6rn?= Engel <joern@purestorage.com>
Subject: Re: [PATCH] mm: add resched points to
 remap_pmd_range/ioremap_pmd_range
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To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>, Spencer Baugh <sbaugh@catern.com>, Toshi Kani <toshi.kani@hp.com>, Andrew Morton <akpm@linux-foundation.org>, Fengguang Wu <fengguang.wu@intel.com>, Joern Engel <joern@logfs.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>, Shachar Raindel <raindel@mellanox.com>, Boaz Harrosh <boaz@plexistor.com>, Andy Lutomirski <luto@amacapital.net>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrey Ryabinin <a.ryabinin@samsung.com>, Roman Pen <r.peniaev@gmail.com>, Andrey Konovalov <adech.fo@gmail.com>, Eric Dumazet <edumazet@google.com>, Dmitry Vyukov <dvyukov@google.com>, Rob Jones <rob.jones@codethink.co.uk>, WANG Chao <chaowang@redhat.com>, open list <linux-kernel@vger.kernel.org>, "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>, Spencer Baugh <Spencer.baugh@purestorage.com>

On Thu, Jul 30, 2015 at 05:22:55PM +0200, Mike Galbraith wrote:
> 
> I piddled about with the thought that it might be nice to be able to
> sprinkle cond_resched() about to cut rt latencies without wrecking
> normal load throughput, cobbled together a cond_resched_rt().
> 
> On my little box that was a waste of time, as the biggest hits are block
> softirq and free_hot_cold_page_list().

Block softirq is one of our problems as well.  It is a bit of a joke
that __do_softirq() moves work to ksoftirqd after 2ms, but block softirq
can take several 100ms in bad cases.

We could give individual softirqs a time budget.  If they exceed the
budget they should complete, but reassert themselves.  Not sure about
the rest, but that would be pretty simple to implement for block
softirq.

Jorn

--
Happiness isn't having what you want, it's wanting what you have.
-- unknown

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