| Message ID | 200902112127.n1BLR2HX031153@imap1.linux-foundation.org |
|---|---|
| State | Accepted |
| Headers | show |
On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote: > 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. Can't really comment on how well the patch works, but we've also noticed a similar slowdown on our systems during startup, so the idea as such is welcome at any rate. /Ricard -- Ricard Wolf Wanderlöf ricardw(at)axis.com Axis Communications AB, Lund, Sweden www.axis.com Phone +46 46 272 2016 Fax +46 46 13 61 30
Ricard Wanderlof wrote: > On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote: > > >> 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. >> > > Can't really comment on how well the patch works, but we've also noticed a > similar slowdown on our systems during startup, so the idea as such is > welcome at any rate. > I just posted a message to linux-arm-kernel regarding a similar problem I have an at91rm9200 based machine with NAND and JFFS2. I suspected that garbage collection was causing delays of up to 3+ seconds during which time my watchdog patting daemon was not being scheduled ... This was causing the watchdog timer to reset my machine but *only* when it was under significant NAND load i.e. boot time, loading up the main application while GCD was running. My solution was to double the watchdog timeout. Aras
I have also noticed the performance degredation caused by the jffs2 garbage collection. The solution we used to this problem on our product was to do 'pkill -STOP jffs2_gcd' very early in the boot process, then right at the end of my boot script put 'sleep 90 && pkill -CONT jffs2_gcd &' This sped the boot time up a lot. Reuben -----Original Message----- From: linux-mtd-bounces@lists.infradead.org [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of Aras Vaichas Sent: Tuesday, 17 March 2009 12:29 p.m. To: Ricard Wanderlof Cc: dwmw2@infradead.org; akpm@linux-foundation.org; dilinger@debian.org; linux-mtd@lists.infradead.org; dilinger@queued.net Subject: Re: [patch 4/9] jffs2: force the jffs2 GC daemon to behave a bitbetter Ricard Wanderlof wrote: > On Wed, 11 Feb 2009, akpm@linux-foundation.org wrote: > > >> 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. >> > > Can't really comment on how well the patch works, but we've also > noticed a similar slowdown on our systems during startup, so the idea > as such is welcome at any rate. > I just posted a message to linux-arm-kernel regarding a similar problem I have an at91rm9200 based machine with NAND and JFFS2. I suspected that garbage collection was causing delays of up to 3+ seconds during which time my watchdog patting daemon was not being scheduled ... This was causing the watchdog timer to reset my machine but *only* when it was under significant NAND load i.e. boot time, loading up the main application while GCD was running. My solution was to double the watchdog timeout. Aras
diff -puN fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better fs/jffs2/background.c --- a/fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better +++ a/fs/jffs2/background.c @@ -95,13 +95,17 @@ static int jffs2_garbage_collect_thread( spin_unlock(&c->erase_completion_lock); - /* 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. */