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From 9706327002caebe6633c93e605882ea37172ec57 Mon Sep 17 00:00:00 2001
From: Andres Salomon <dilinger@debian.org>
Date: Mon, 3 Nov 2008 01:08:25 +0000
Subject: [PATCH] jffs2-choke-gc-thread.patch
I've noticed some pretty poor behavior on OLPC machines after bootup, when
gdm/X are starting. The GCD monopolizes the scheduler (which in turns means
it gets to do more nand i/o), which results in processes taking much much
longer than they should to start.
As an example, on an OLPC machine going from OFW to a usable X (via auto-login
gdm) takes 2m 30s. The majority of this time is consumed by the switch into
graphical mode. With this patch, we cut a full 60s off of bootup time. After
bootup, things are much snappier as well.
Note that we have seen a CRC node error with this patch that causes the machine
to fail to boot, but we've also seen that problem without this patch.
Signed-off-by: Andres Salomon <dilinger@debian.org>
---
fs/jffs2/background.c | 18 +++++++++++-------
1 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/fs/jffs2/background.c b/fs/jffs2/background.c
index 8adebd3..f38d557 100644
--- a/fs/jffs2/background.c
+++ b/fs/jffs2/background.c
@@ -95,13 +95,17 @@ static int jffs2_garbage_collect_thread(void *_c)
schedule();
}
- /* This thread is purely an optimisation. But if it runs when
- other things could be running, it actually makes things a
- lot worse. Use yield() and put it at the back of the runqueue
- every time. Especially during boot, pulling an inode in
- with read_inode() is much preferable to having the GC thread
- get there first. */
- yield();
+ /* Problem - immediately after bootup, the GCD spends a lot
+ * of time in places like jffs2_kill_fragtree(); so much so
+ * that userspace processes (like gdm and X) are starved
+ * despite plenty of cond_resched()s and renicing. Yield()
+ * doesn't help, either (presumably because userspace and GCD
+ * are generally competing for a higher latency resource -
+ * disk).
+ * This forces the GCD to slow the hell down. Pulling an
+ * inode in with read_inode() is much preferable to having
+ * the GC thread get there first. */
+ schedule_timeout_interruptible(msecs_to_jiffies(50));
/* Put_super will send a SIGKILL and then wait on the sem.
*/
--
1.5.6.5
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