linux-kernel - Re: [Patch 00/15] Reduce tracing payload size.

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Message-ID: <AANLkTin9=zCbfwdt0GxaGMynTqUsf8R4GWJy88qw87A_@mail.gmail.com>
Date:	Mon, 6 Dec 2010 17:31:04 +0100
From:	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"Ted Ts'o" <tytso@....edu>, David Sharp <dhsharp@...gle.com>,
	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mrubin@...gle.com
Subject: Re: [Patch 00/15] Reduce tracing payload size.

On Mon, Dec 6, 2010 at 3:58 PM, Andi Kleen <andi@...stfloor.org> wrote:
> On Mon, Dec 06, 2010 at 08:56:37AM -0500, Ted Ts'o wrote:
>> On Mon, Dec 06, 2010 at 02:22:00PM +0100, Andi Kleen wrote:
>> > David Sharp <dhsharp@...gle.com> writes:
>> > >
>> > > These patches are just a start to shrinking the size of trace events. I am
>> > > planning to also make small versions of trace events that are used when
>> > > CONFIG_SMALL_TRACES is enabled. I'm also open to discussion of other ways to
>> > > shrink event sizes.
>> >
>> > Maybe the simplest would be to lzo them as they get logged?
>> > I assume you already considered that?
>>
>> The tracing subsystem is supposed to be extremely low-overhead.
>> Compressiong the event log would add considerable CPU overhead.  If we
>
> lzo as a rule of thumb is about as expensive as 3x memcpy()
> That's not really expensive.

That is true for the decompression step but not for the compression
one, which takes more than 10 memcpys().

>
> -Andi
>
> --
> ak@...ux.intel.com -- Speaking for myself only.
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