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

[Miguel Ojeda]

On Mon, Dec 6, 2010 at 3:58 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> 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@xxxxxxxxxx> 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
>
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> ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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