Re: [PATCH] sched: Fix adverse effects of NFS client on interactive response

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Trond Myklebust wrote:
On Wed, 2005-12-21 at 17:00 +1100, Peter Williams wrote:

This patch addresses the adverse effect that the NFS client can have on interactive response when CPU bound tasks (such as a kernel build) operate on files mounted via NFS. (NB It is emphasized that this has nothing to do with the effects of interactive tasks accessing NFS mounted files themselves.)

The problem occurs because tasks accessing NFS mounted files for data can undergo quite a lot of TASK_INTERRUPTIBLE sleep depending on the load on the server and the quality of the network connection. This can result in these tasks getting quite high values for sleep_avg and consequently a large priority bonus. On the system where I noticed this problem they were getting the full 10 bonus points and being given the same dynamic priority as genuine interactive tasks such as the X server and rythmbox.

The solution to this problem is to use TASK_NONINTERACTIVE to tell the scheduler that the TASK_INTERRUPTIBLE sleeps in the NFS client and SUNRPC are NOT interactive sleeps.


Sorry. That theory is just plain wrong. ALL of those case _ARE_
interactive sleeps.

It's not a theory. It's a result of observing a -j 16 build with the sources on an NFS mounted file system with top with and without the patches and comparing that with the same builds with the sources on a local file system. Without the patches the tasks in the kernel build all get the same dynamic priority as the X server and other interactive programs when the sources are on an NFS mounted file system. With the patches they generally have dynamic priorities between 6 to 10 higher than the X server and other interactive programs.

In both cases, when the build is run on a source on a local file system the kernel build tasks all have dynamic priorities 6 to 10 higher than the X server and other interactive programs.

In all cases, the dynamic priorities of the X server and other interactive programs are the same.

In the testing that I have done so far the patch has not resulted in any genuine interactive tasks not being identified as interactive.


Peter
PS There's a difference between interruptible and interactive in that while all interactive sleeps will be interruptible not all interruptible sleeps are interactive. Ingo introduced TASK_NONINTERACTIVE to enable this distinction to be made.
--
Peter Williams                                   [email protected]

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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