From: erik quanstrom <quanstro@quanstro.net>
To: 9fans@9fans.net
Subject: Re: [9fans] interesting timing tests
Date: Tue, 22 Jun 2010 21:09:01 -0400 [thread overview]
Message-ID: <370f0af00a45e85654888bdbc1deebe9@kw.quanstro.net> (raw)
In-Reply-To: <p0624081dc845d03ca048@[192.168.0.7]>
> Do you have a way to turn off one of the sockets on "c" (2 x E5540) and get the numbers with HT (8 processors) and without HT (4 processors)? It would also be interesting to see "c" with HT turned off.
here's the progression
4 4.41u 1.83s 4.06r 0. %ilock
8 4.47u 2.37s 3.60r 2.0
12 4.49u 8.34s 4.40r 11.0
16 4.36u 13.16s 4.43r 14.7
here's a fun little calculation:
16 threads * 4.43 s * 0.147 + 1.83s baseline
= 10.41936 + 1.83 thread*s
= 12.25s
it seems that increased ilock contention is a big factor
in the increase in system time.
ilock accounting has most (>80%) long-held ilocks
(>8.5µs, ~21k cycles) starting here /sys/src/libc/port/pool.c:1318.
this is no surprise. technically, a long-held ilock is not
really a problem—until somebody else wants it. but we
can be fairly certain that allocb/malloc is a fairly contended code
path.
hopefully i'll be able to test a less-contended replacement for
allocb/freeb before i run out of time with this machine.
> Certainly it seems to me that idlehands needs to be fixed,
> your bit array "active.schedwait" is one way.
i'm not convinced that idlehands is anything but a power-waster.
performance wise, it's nearly ideal.
- erik
prev parent reply other threads:[~2010-06-23 1:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-18 23:26 erik quanstrom
2010-06-19 13:42 ` Richard Miller
2010-06-20 1:36 ` erik quanstrom
2010-06-20 7:44 ` Richard Miller
2010-06-20 12:45 ` erik quanstrom
2010-06-20 16:51 ` Richard Miller
2010-06-20 21:55 ` erik quanstrom
2010-06-21 1:41 ` erik quanstrom
2010-06-21 3:46 ` Venkatesh Srinivas
2010-06-21 14:40 ` erik quanstrom
2010-06-21 16:42 ` Venkatesh Srinivas
2010-06-21 16:43 ` erik quanstrom
2010-06-21 21:11 ` Bakul Shah
2010-06-21 21:21 ` erik quanstrom
2010-06-21 21:47 ` Bakul Shah
2010-06-21 22:16 ` erik quanstrom
2010-06-22 3:24 ` Lawrence E. Bakst
2010-06-23 1:09 ` erik quanstrom [this message]
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