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Date: Wed, 12 Jun 2013 10:50:01 -0700
From: Davidlohr Bueso <davidlohr.bueso@...com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...e.hu>,
赖江山 <laijs@...fujitsu.com>,
Dipankar Sarma <dipankar@...ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Triplett <josh@...htriplett.org>, niv@...ibm.com,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Valdis Kletnieks <Valdis.Kletnieks@...edu>,
David Howells <dhowells@...hat.com>,
Eric Dumazet <edumazet@...gle.com>,
Darren Hart <darren@...art.com>,
Frédéric Weisbecker <fweisbec@...il.com>,
sbw@....edu
Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock
On Tue, 2013-06-11 at 14:10 -0400, Steven Rostedt wrote:
> Perhaps short work loads have a cold cache, and the impact on cache is
> not as drastic?
>
> It would be interesting to see what perf reports on these runs.
After running the aim7 workloads on Paul's v3 patch (same 80 core, 8
socket box - HT off) the results are quite similar to the v1. One
difference is that the five_sec workload benefited with +15% throughput
after 500 users.
Taking a further look at each workload:
* five_sec: spends a large amount of time in the newish mcs style lock
at the spin on owner for the inode->i_mutex:
24.13% 315655 reaim [kernel.kallsyms] [k] mspin_lock
|
--- mspin_lock
|
|--99.76%-- __mutex_lock_killable_slowpath
| mutex_lock_killable
| vfs_readdir
| SyS_getdents
| system_call_fastpath
| __getdents64
With this patch:
23.56% 310531 reaim [kernel.kallsyms] [k] mspin_lock
|
--- mspin_lock
|
|--99.78%-- __mutex_lock_killable_slowpath
| mutex_lock_killable
| vfs_readdir
| SyS_getdents
| system_call
| __getdents64
* custom: Got a -33% throughput regression with this patch with 10-100
users and -46% with 100 users and up. It spends most kernel space time
dealing trying to take the inode->i_mutex and the ext4 ->s_orphan_lock
(note that all runs are performed on ramdisks with ext4):
3.12% 137131 reaim [kernel.kallsyms] [k] mspin_lock
|
--- mspin_lock
|
|--82.98%-- __mutex_lock_killable_slowpath
| mutex_lock_killable
| vfs_readdir
| SyS_getdents
| system_call_fastpath
| __getdents64
|
|--16.97%-- __mutex_lock_slowpath
| mutex_lock
| |
| |--47.65%-- ext4_orphan_del
| |--45.01%-- ext4_orphan_add
With this patch:
2.14% 109982 reaim [kernel.kallsyms] [k] mspin_lock
|
--- mspin_lock
|
|--68.67%-- __mutex_lock_killable_slowpath
| mutex_lock_killable
| vfs_readdir
| SyS_getdents
| system_call
| __getdents64
|
|--31.24%-- __mutex_lock_slowpath
| mutex_lock
| |
| |--40.36%-- ext4_orphan_del
* short: is the big winner for this patch, +69% throughput improvement
with 100-2000 users. This makes a lot of sense since the workload spends
a ridiculous amount of time trying to acquire the d_lock:
84.86% 1569902 reaim [kernel.kallsyms] [k] _raw_spin_lock
|
--- _raw_spin_lock
|
|--49.96%-- dget_parent
| __fsnotify_parent
|--49.71%-- dput
| |
| |--99.98%-- __fsnotify_parent
With this patch:
70.65% 467422 reaim [kernel.kallsyms] [k] tkt_q_do_spin
|
--- tkt_q_do_spin
|
|--100.00%-- tkt_spin_pass
| |
| |--100.00%-- _raw_spin_lock
| | |
| | |--50.07%-- dget_parent
| | | __fsnotify_parent
| | |--49.93%-- dput
| | | __fsnotify_parent
* disk: This patch benefits when adding more concurrency. Got -57% with
10-100 users, -25% with 100-1000 users and +8% with over 1000 users.
Spends a good amount of time dealing with the wait_queue lock. The perf
traces are with 80 users, where we see the worst numbers:
22.34% 20400 reaim [kernel.kallsyms] [k] _raw_spin_lock_irqsave
|
--- _raw_spin_lock_irqsave
|
|--50.28%-- __wake_up
| |
| |--99.10%-- __wake_up_bit
| | wake_up_bit
| | unlock_buffer
|
|--33.73%-- prepare_to_wait_exclusive
| __wait_on_bit_lock
| out_of_line_wait_on_bit_lock
| __lock_buffer
| do_get_write_access
| jbd2_journal_get_write_access
| __ext4_journal_get_write_access
|--14.76%-- finish_wait
| |
| |--98.93%-- __wait_on_bit_lock
| | out_of_line_wait_on_bit_lock
| | __lock_buffer
| | do_get_write_access
| | jbd2_journal_get_write_access
| | __ext4_journal_get_write_access
With this patch the the time spent in the mentioned spinlocks
considerably reduced:
8.09% 6237 reaim [kernel.kallsyms] [k] __read_lock_failed
|
--- __read_lock_failed
_raw_read_lock
|
|--99.08%-- start_this_handle
| jbd2__journal_start
| __ext4_journal_start_sb
1.48% 1032 reaim [kernel.kallsyms] [k] _raw_spin_lock_irqsave
|
--- _raw_spin_lock_irqsave
|
|--50.77%-- prepare_to_wait
| |
| |--72.61%-- jbd2_log_wait_commit
| | jbd2_complete_transaction
|--21.76%-- prepare_to_wait_exclusive
| __wait_on_bit_lock
| out_of_line_wait_on_bit_lock
| __lock_buffer
| do_get_write_access
| jbd2_journal_get_write_access
|--11.46%-- __wake_up
| |
| |--44.21%-- ftrace_define_fields_jbd2_run_stats
| | __ext4_journal_stop
|--10.39%-- finish_wait
| |
| |--53.18%-- __wait_on_bit_lock
| | out_of_line_wait_on_bit_lock
| | __lock_buffer
| | do_get_write_access
| | jbd2_journal_get_write_access
| | __ext4_journal_get_write_access
Thanks,
Davidlohr
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