lkml.org 
[lkml]   [2006]   [Jul]   [31]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateMon, 31 Jul 2006 03:57:16 -0700 (PDT)
SubjectRe: [RFC 1/4] kevent: core files.
FromDavid Miller <>
From: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Date: Mon, 31 Jul 2006 14:50:37 +0400

> 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.

Do you know how many cachelines are dirtied by system call
entry and exit on typical system?

On sparc64 it is a minimum of 3 64-byte cachelines just to save and
restore the system call time cpu register state.  If application is
deep in a call chain, register windows might spill and each such
register window will dirty 2 more cachelines as they are dumped to the
stack.

I am not even talking about the other basic necessities of doing
a system call such as touching various task_struct and thread_info
state to check for pending signals etc.

System call overhead is non-trivial especially when you are using
it to move only a few small objects into and out of the kernel.

So I would say for up to 4 or 5 events, system call overhead alone
touches as many cache lines as the events themselves.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-07-31 12:59    [from the cache]
©2003-2008