From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Chan" Subject: Re: Why are network counters only updated once a second? Date: Mon, 14 Jan 2008 14:31:49 -0800 Message-ID: <1200349909.15122.31.camel@dell> References: <478BC662.6030004@hp.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: "netdev" To: "Mark Seger" Return-path: Received: from mms1.broadcom.com ([216.31.210.17]:4085 "EHLO mms1.broadcom.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755821AbYANVpG (ORCPT ); Mon, 14 Jan 2008 16:45:06 -0500 In-Reply-To: <478BC662.6030004@hp.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2008-01-14 at 15:30 -0500, Mark Seger wrote: > Eventually the frequency became better aligned at a 1 second interval > because now the number look better, but the problem I see is that when > the sampling interval is very close to the monitoring interval you still > get periodic incorrect data. Furthermore, you now need to know which > way the counters are updated before you pick a sampling interval! But > the real point is if anyone ever wants to do finer grained monitoring, > say every 1/2 or even tenth of a second, they can't because the counters > won't change between samples. Has this ever been discussed before? On most Broadcom NICs, the statistics counters are periodically DMA'ed from the chip and the default interval is roughly 1 second. On most of these chips, you can override this interval using ethtool -C eth0. As I mentioned earlier, the 5706/5708 has a bug in the statistics DMA engine that can corrupt counters from time to time. The workaround is effective, but you now lose the ability to control the DMA interval.