linux-kernel - Re: [RFC 1/4] kevent: core files.

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Message-ID: <20060731105037.GA2073@2ka.mipt.ru>
Date:	Mon, 31 Jul 2006 14:50:37 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	drepper@...hat.com, zach.brown@...cle.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC 1/4] kevent: core files.

On Mon, Jul 31, 2006 at 08:35:55PM +1000, Herbert Xu (herbert@...dor.apana.org.au) wrote:
> Evgeniy Polyakov <johnpol@....mipt.ru> wrote:
> >
> >> - if there is space, report it in the ring buffer.  Yes, the buffer
> >>   can be optional, then all events are reported by the system call.
> > 
> > That requires a copy, which can neglect syscall overhead.
> > Do we really want it to be done?
> 
> Please note that we're talking about events here, not actual data.  So
> only the event is being copied, which is presumably rather small compared
> to the data.

In syscall time kevents copy 40bytes for each event + 12 bytes of header 
(number of events, timeout and command number). That's likely two cache
lines if only one event is reported.

-- 
	Evgeniy Polyakov
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