From: Arnd Bergmann <arnd@arndb•de>
To: Carl Love <cel@us•ibm.com>
Cc: linuxppc-dev@ozlabs•org, cbe-oss-dev@ozlabs•org,
oprofile-list@lists•sourceforge.net,
linux-kernel@vger•kernel.org
Subject: Re: [Cbe-oss-dev] [RFC, PATCH] CELL Oprofile SPU profiling updated patch
Date: Thu, 15 Feb 2007 22:03:59 +0100 [thread overview]
Message-ID: <200702152203.59902.arnd@arndb.de> (raw)
In-Reply-To: <1171570918.31179.36.camel@dyn9047021078.beaverton.ibm.com>
On Thursday 15 February 2007 21:21, Carl Love wrote:
> I have done some quick measurements. =A0The above method limits the loop
> to at most 2^16 iterations. =A0Based on running the algorithm in user
> space, it takes about 3ms of computation time to do the loop 2^16 times.
>=20
> At the vary least, we need to put the resched in say every 10,000
> iterations which would be about every 0.5ms. =A0Should we do a resched
> more often? =A0
Yes, just to be on the safe side, I'd suggest to do it every 1000
iterations.
=20
> Additionally we could up the size of the table to 512 which would reduce
> the maximum time to about 1.5ms. =A0What do people think about increasing
> the table size?
No, that won't help too much. I'd say 256 or 128 entries is the most
we should have.
> As for using a logarithmic spacing of the precomputed values, this
> approach means that the space between the precomputed values at the high
> end would be much larger then 2^14, assuming 256 precomputed values.
> That means it could take much longer then 3ms to get the needed LFSR
> value for a large N. =A0By evenly spacing the precomputed values, we can
> ensure that for all N it will take less then 3ms to get the value.
> Personally, I am more comfortable with a hard limit on the compute time
> then a variable time that could get much bigger then the 1ms threshold
> that Arnd wants for resched. =A0Any thoughts?
When using precomputed values on a logarithmic scale, I'd recommend
just rounding to the closest value and accepting the relative inaccuracy,
instead of using the precomputed value as the base and then calculating
from there.
Arnd <><
next prev parent reply other threads:[~2007-02-15 21:03 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-14 23:52 [Cbe-oss-dev] [RFC, PATCH] CELL Oprofile SPU profiling updated patch Carl Love
2007-02-15 14:37 ` Arnd Bergmann
2007-02-15 16:15 ` Maynard Johnson
2007-02-15 18:13 ` Arnd Bergmann
2007-02-15 20:21 ` Carl Love
2007-02-15 21:03 ` Arnd Bergmann [this message]
2007-02-15 21:50 ` Paul E. McKenney
2007-02-16 0:33 ` Arnd Bergmann
2007-02-16 0:32 ` Maynard Johnson
2007-02-16 17:14 ` Arnd Bergmann
2007-02-16 21:43 ` Maynard Johnson
2007-02-18 23:18 ` Maynard Johnson
-- strict thread matches above, loose matches on Subject: below --
2007-02-22 0:02 Carl Love
2007-02-26 23:50 ` Arnd Bergmann
2007-02-27 1:31 ` Michael Ellerman
2007-02-27 16:52 ` Maynard Johnson
2007-02-28 1:44 ` Arnd Bergmann
2007-02-06 0:28 [RFC,PATCH] CELL PPU " Carl Love
2007-02-06 23:02 ` [Cbe-oss-dev] [RFC, PATCH] CELL " Carl Love
2007-02-07 15:41 ` Maynard Johnson
2007-02-07 22:48 ` Michael Ellerman
2007-02-08 15:03 ` Maynard Johnson
2007-02-08 14:18 ` Milton Miller
2007-02-08 17:21 ` Arnd Bergmann
2007-02-08 18:01 ` Adrian Reber
2007-02-08 22:51 ` Carl Love
2007-02-09 2:46 ` Milton Miller
2007-02-09 16:17 ` Carl Love
2007-02-11 22:46 ` Milton Miller
2007-02-12 16:38 ` Carl Love
2007-02-09 18:47 ` Milton Miller
2007-02-09 19:10 ` Arnd Bergmann
2007-02-09 19:46 ` Milton Miller
2007-02-08 23:59 ` Maynard Johnson
2007-02-09 18:03 ` Milton Miller
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