From owner-freebsd-alpha Sun Jun 3 17:42:43 2001 Delivered-To: freebsd-alpha@freebsd.org Received: from netau1.alcanet.com.au (ntp.alcanet.com.au [203.62.196.27]) by hub.freebsd.org (Postfix) with ESMTP id 74FB737B401 for ; Sun, 3 Jun 2001 17:42:37 -0700 (PDT) (envelope-from jeremyp@gsmx07.alcatel.com.au) Received: from mfg1.cim.alcatel.com.au (mfg1.cim.alcatel.com.au [139.188.23.1]) by netau1.alcanet.com.au (8.9.3 (PHNE_22672)/8.9.3) with ESMTP id KAA20676 for ; Mon, 4 Jun 2001 10:42:35 +1000 (EST) Received: from gsmx07.alcatel.com.au by cim.alcatel.com.au (PMDF V5.2-32 #37640) with ESMTP id <01K4D6VAUHM8VLKPBQ@cim.alcatel.com.au> for freebsd-alpha@FreeBSD.ORG; Mon, 4 Jun 2001 10:42:34 +1000 Received: (from jeremyp@localhost) by gsmx07.alcatel.com.au (8.11.1/8.11.1) id f540gWl72059 for freebsd-alpha@FreeBSD.ORG; Mon, 04 Jun 2001 10:42:32 +1000 (EST envelope-from jeremyp) Content-return: prohibited Date: Mon, 04 Jun 2001 10:42:32 +1000 From: Peter Jeremy Subject: Re: Abyssmal interrupt latency with -current In-reply-to: <20010531093454.X89950@gsmx07.alcatel.com.au>; from peter.jeremy@alcatel.com.au on Thu, May 31, 2001 at 09:34:54AM +1000 To: freebsd-alpha@FreeBSD.ORG Mail-Followup-To: freebsd-alpha@FreeBSD.ORG Message-id: <20010604104232.V89950@gsmx07.alcatel.com.au> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii Content-disposition: inline User-Agent: Mutt/1.2.5i References: <20010531093454.X89950@gsmx07.alcatel.com.au> Sender: owner-freebsd-alpha@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org On 2001-May-31 09:34:54 +1000, Peter Jeremy wrote: >I've recently been getting SILO overflows on the PPP link on my >Multia. I recall seeing a comment (probably in -current) about >interrupt latency regressions, but the Multia seems worse than >my 486, so I suspect some of it is alpha-specific. And I found that it is... see alpha/27866. Basically `fast' interrupts aren't detected as fast and are being scheduled as threads. Note that this bug would have been detected by the compiler if we were using a type-safe language. >The median time from entering XentInt to the start of the sio >interrupt handler is 61usec. With my fix in, the mean and median both drop to just over 21usec, with a range of 10..~129 usec. The worst case is fairly bad, but is good enough to allow sio to work. The reason for the large worst-case latencies are nested interrupts - especially clock interrupts. (These figures are for a UP, not SMP kernel). >Overall, I suspect I'd be better off ignoring all interrupts except >the clock interrupt and polling everything everything else from >within the clock interrupt. I'm still considering this. The only problem I see is for receiving lots of small ethernet frames (the Multia only supports 10Mbps, so a large frame takes >1msec). Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message