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Date: Mon, 26 Sep 2011 17:39:31 -0700
From: Simon Kirby <sim@...tway.ca>
To: Trond Myklebust <Trond.Myklebust@...app.com>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: NFS client growing system CPU
Hello!
Following up on "System CPU increasing on idle 2.6.36", this issue is
still happening even on 3.1-rc7. So, since it has been 9 months since I
reported this, I figured I'd bisect this issue. The first bisection ended
in an IPMI regression that looked like the problem, so I had to start
again. Eventually, I got commit b80c3cb628f0ebc241b02e38dd028969fb8026a2
which made it into 2.6.34-rc4.
With this commit, system CPU keeps rising as the log crunch box runs
(reads log files via NFS and spews out HTML files into NFS-mounted report
directories). When it finishes the daily run, the system time stays
non-zero and continues to be higher and higher after each run, until the
box never completes a run within a day due to all of the wasted cycles.
I previously posted a munin CPU graph picture here:
http://0x.ca/sim/ref/2.6.36/cpu_logcrunch_nfs.png
Here is the most recent graph of me bisecting, roughly one day at a time:
http://0x.ca/sim/ref/2.6.34/cpu.png
Running a kernel built on this commit, I can actually make the problem
stop by just typing "sync". CPU then goes down to 0 and everything is
fine. Future kernel versions, such as 2.6.36, do not change with just a
"sync", but "sync;echo 3 > /proc/sys/vm/drop_caches;sync" _does_ stop
the system CPU usage. I can bisect this change, too, if that would help.
Here is the commit:
commit b80c3cb628f0ebc241b02e38dd028969fb8026a2
Author: Trond Myklebust <Trond.Myklebust@...app.com>
Date: Fri Apr 9 19:07:07 2010 -0400
NFS: Ensure that writeback_single_inode() calls write_inode() when syncing
Since writeback_single_inode() checks the inode->i_state flags _before_ it
flushes out the data, we need to ensure that the I_DIRTY_DATASYNC flag is
already set. Otherwise we risk not seeing a call to write_inode(), which
again means that we break fsync() et al...
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 53ff70e..7f40ea3 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -421,6 +421,7 @@ static void
nfs_mark_request_dirty(struct nfs_page *req)
{
__set_page_dirty_nobuffers(req->wb_page);
+ __mark_inode_dirty(req->wb_page->mapping->host, I_DIRTY_DATASYNC);
}
#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
@@ -660,6 +661,7 @@ static int nfs_writepage_setup(struct nfs_open_context *ctx, struct page *page,
req = nfs_setup_write_request(ctx, page, offset, count);
if (IS_ERR(req))
return PTR_ERR(req);
+ nfs_mark_request_dirty(req);
/* Update file length */
nfs_grow_file(page, offset, count);
nfs_mark_uptodate(page, req->wb_pgbase, req->wb_bytes);
@@ -739,8 +741,6 @@ int nfs_updatepage(struct file *file, struct page *page,
status = nfs_writepage_setup(ctx, page, offset, count);
if (status < 0)
nfs_set_pageerror(page);
- else
- __set_page_dirty_nobuffers(page);
dprintk("NFS: nfs_updatepage returns %d (isize %lld)\n",
status, (long long)i_size_read(inode));
With the build before this commit, the system time stays low always and
returns to 0% after every daily run.
Simon-
On Wed, Dec 08, 2010 at 04:53:09PM -0500, Trond Myklebust wrote:
> On Wed, 2010-12-08 at 13:25 -0800, Simon Kirby wrote:
> > Possibly related to the flush-processes-taking-CPU issues I saw
> > previously, I thought this was interesting. I found a log-crunching box
> > that does all of its work via NFS and spends most of the day sleeping.
> > It has been using a linearly-increasing amount of system time during the
> > time where is sleeping. munin graph:
> >
> > http://0x.ca/sim/ref/2.6.36/cpu_logcrunch_nfs.png
> >
> > top shows:
> >
> > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> > 4767 root 20 0 0 0 0 S 16 0.0 2413:29 flush-0:69
> > 22385 root 20 0 0 0 0 S 10 0.0 1320:23 flush-0:70
> > (rest idle)
> >
> > perf top shows:
> >
> > -------------------------------------------------------------------------------------------
> > PerfTop: 252 irqs/sec kernel:97.2% exact: 0.0% [1000Hz cycles], (all, 2 CPUs)
> > -------------------------------------------------------------------------------------------
> >
> > samples pcnt function DSO
> > _______ _____ _______________________________ ___________
> >
> > 912.00 21.2% _raw_spin_lock [kernel]
> > 592.00 13.8% nfs_writepages [kernel]
> > 474.00 11.0% queue_io [kernel]
> > 428.00 10.0% writeback_single_inode [kernel]
> > 379.00 8.8% writeback_sb_inodes [kernel]
> > 237.00 5.5% bit_waitqueue [kernel]
> > 184.00 4.3% do_writepages [kernel]
> > 169.00 3.9% __iget [kernel]
> > 132.00 3.1% redirty_tail [kernel]
> > 85.00 2.0% iput [kernel]
> > 72.00 1.7% _atomic_dec_and_lock [kernel]
> > 67.00 1.6% write_cache_pages [kernel]
> > 63.00 1.5% port_inb [ipmi_si]
> > 62.00 1.4% __mark_inode_dirty [kernel]
> > 48.00 1.1% __wake_up_bit [kernel]
> > 32.00 0.7% nfs_write_inode [kernel]
> > 26.00 0.6% native_read_tsc [kernel]
> > 25.00 0.6% radix_tree_gang_lookup_tag_slot [kernel]
> > 25.00 0.6% schedule [kernel]
> > 24.00 0.6% wake_up_bit [kernel]
> > 20.00 0.5% apic_timer_interrupt [kernel]
> > 19.00 0.4% ia32_syscall [kernel]
> > 16.00 0.4% find_get_pages_tag [kernel]
> > 15.00 0.3% _raw_spin_lock_irqsave [kernel]
> > 15.00 0.3% load_balance [kernel]
> > 13.00 0.3% ktime_get [kernel]
> > 12.00 0.3% shrink_icache_memory [kernel]
> > 11.00 0.3% semop libc-2.7.so
> > 9.00 0.2% nfs_pageio_doio [kernel]
> > 8.00 0.2% dso__find_symbol perf
> > 8.00 0.2% down_read [kernel]
> > 7.00 0.2% __switch_to [kernel]
> > 7.00 0.2% __phys_addr [kernel]
> > 7.00 0.2% nfs_pageio_init [kernel]
> > 7.00 0.2% pagevec_lookup_tag [kernel]
> > 7.00 0.2% _cond_resched [kernel]
> > 7.00 0.2% up_read [kernel]
> > 6.00 0.1% sched_clock_local [kernel]
> > 5.00 0.1% rb_erase [kernel]
> > 5.00 0.1% page_fault [kernel]
> >
> > "tcpdump -i any -n port 2049" and "nfsstat" shows this work does not actually result
> > in any NFS packets.
> >
> > Known 2.6.36 issue? This did not occur on 2.6.35.4, according to the
> > munin graphs. I'll try 2.6.37-rc an see if it changes.
>
> Possibly a side effect of the fs/fs-writeback.c changes in 2.6.36? You
> do appear to be hitting a lot of spinlock contention, but I suspect that
> a lot of it is coming from writeback_sb_inodes, writeback_single_inode
> and queue_io, all of which seem unnaturally high on your stats above.
>
> I don't see how you can be seeing no traffic on the wire. You are
> certainly hitting some page writeout (0.2% nfs_pageio_doio).
>
> Cheers
> Trond
> --
> Trond Myklebust
> Linux NFS client maintainer
>
> NetApp
> Trond.Myklebust@...app.com
> www.netapp.com
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