On Thu, Apr 13, 2006 at 05:26:39PM +0200, Laurent Vivier wrote:
> Le lun 10/04/2006 à 10:24, Andrew Morton a écrit :
> > Laurent Vivier <[email protected]> wrote:
> > >
> > > Does the attached patch look like the thing you though about ?
> >
> > I guess so. But it'll need a lot of performance testing on big SMP
> > to work out what the impact is.
>
> I made some tests with dbench:
>
> IBM x440: 8 CPUs hyperthreaded = 16 CPUs (Xeon at 1.4 Ghz)
>
I ran the same tests on a 16 core EM64T box very similar to the one you ran
dbench on :). Dbench results on ext3 varies quite a bit. I couldn't get
to a statistically significant conclusion For eg,
With atomic counters, 32 clients, 3 runs
Throughput 187.712 MB/sec 32 procs
Throughput 197.059 MB/sec 32 procs
Throughput 203.522 MB/sec 32 procs
Without atomic counters (per-cpu counters), 32 clients, 3 runs
Throughput 228.805 MB/sec 32 procs
Throughput 155.831 MB/sec 32 procs
Throughput 134.777 MB/sec 32 procs
The oprofile profiles for the atomic counter case looks like this:
CPU: P4 / Xeon with 2 hyper-threads, speed 3002.77 MHz (estimated)
Counted GLOBAL_POWER_EVENTS events (time during which processor is not
stopped) with a unit mask of 0x01 (mandatory) count 100000
samples % app name symbol name
180505286 57.7844 vmlinux-t poll_idle
51944524 16.6288 vmlinux-t ext3_test_allocatable
43648955 13.9731 vmlinux-t bitmap_search_next_usable_block
2892251 0.9259 vmlinux-t copy_user_generic
2099969 0.6723 vmlinux-t do_get_write_access
1459523 0.4672 vmlinux-t journal_dirty_metadata
1393413 0.4461 vmlinux-t journal_stop
So the atomic counters in question are not even hotspots on this workload,
so IMHO, dbench cannot be used to come to any conclusion regarding per-cpu
counters vs atomics here.
Thanks,
Kiran
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