From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Route cache performance under stress Date: Tue, 10 Jun 2003 18:15:36 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <3EE682B8.8060708@candelatech.com> References: <20030610.152020.59678979.davem@redhat.com> <3EE67D2D.80608@candelatech.com> <20030610.180120.71112140.davem@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: To: "David S. Miller" , "'netdev@oss.sgi.com'" In-Reply-To: <20030610.180120.71112140.davem@redhat.com> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org David S. Miller wrote: > From: Ben Greear > Date: Tue, 10 Jun 2003 17:51:57 -0700 > > Maybe as a configurable option, since it would make tcpdump less useful. > Seems like we could kludge it up so that we used the TSC (or whatever that > really fast hardware clock is) to provide some relative stamp that could be > converted to a time_val later? > > I have a strange feeling that Ralph's system isn't using > TSC and that's why it shows up so high on the profiles :-) > TSC do_gettimeofday() is REALLY cheap (TSC read plus a multiply which > x86 does in like 5 cycles). > > Yes, this idea has been tossed around before. But what's funny > is that on the bigger boxes, you don't use TSC because amongst > the different nodes of the machine they are skewed, so you have > to use the ACPI timer or something like that for timestamping. What determines whether or not we use the "TSC do_gettimeofday". Does it automagically happen when you compile for P-III or something like that? And how big of a "bigger box" are you talking about...regular old SMP, or NUMA? > > It does seem a bit wasteful to do the gettimeofday when most of the time > the result is ignored. > > (Or, are there things other than tcpdump that need the gettimeofday stamp?) > > SO_RECVSTAMP, any socket on the machine can ask for this. Do we know when we are being asked for this value? Ie, could we do the TSC/ACPI timer -> time_val conversion here? If TSC means cheap gettimeofday anyway, then my last question is moot. Thanks, Ben -- Ben Greear President of Candela Technologies Inc http://www.candelatech.com ScryMUD: http://scry.wanfear.com http://scry.wanfear.com/~greear