Date: Sat, 1 Jan 2000 05:14:05 +0000 (GMT) From: Mike Silbersack <silby@silby.com> To: <freebsd-current@freebsd.org> Subject: Some interrupt coalescing tests Message-ID: <20000101045805.G4587-200000@patrocles.silby.com>
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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. Send mail to mime@docserver.cac.washington.edu for more info. --0-419118699-946703556=:4587 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Content-ID: <20000101051245.S4587@patrocles.silby.com> Well, I've been watching everyone argue about the value of interrupt coalescing in the net drivers, so I decided to port terry's patch to 4.4 & -current to see what the results are. The patch included applies cleanly to 4.4's if_dc, and will apply to -current with a one line change. Whitespace is horrible, I copied and pasted the original patch, used patch -l, etc. The test setup I used was as follows: Duron 600, PNIC, running -current Celeron 450, ADMtek tulip-clone, running -stable The network is 100mbps, switched. To simulate load, I used a syn flooder aimed at an unused port. icmp/rst response limiting was enabled. With the -current box attacking the -stable box, I was able to notice a slight drop in interrupts/second with the patch applied. The number of packets was ~57000/second. Before: ~46000 ints/sec, 57-63% processor usage due to interrupts. After: ~38000 ints/sec, 50-60% processor usage due to interrupts. In both cases, the box felt responsive. With the -stable box attacking the -current box, the patch made no difference. The box bogged down at only ~25000 ints/sec, and response limiting reported the number of packets to be ~44000/second. I'm not sure if the number was lower because the celeron couldn't run the flooder as quickly, or if the -current box was dropping packets. I suspect the latter, as the -current box was NOTICEABLY slowed down; I could watch systat refresh the screen. The conclusion? I think that the dc driver does a good enough job of grabbing multiple packets at once, and won't be helped by Terry's patch except in a few very cases. In fact, I have a sneaky suspicion that Terry's patch may increase bus traffic slightly. I'm not sure how much of an issue this is, perhaps Bill or Luigi could comment. In short, if we're going to try to tackle high interrupt load, it should be done by disabling interrupts and going to polling under high load; the patch proposed here isn't worth the extra complexity. I suppose this would all change if we were using LRP and doing lots of processing in the interrupt handler... but we aren't. Mike "Silby" Silbersack --0-419118699-946703556=:4587 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII; NAME="if_dc.diff" Content-Transfer-Encoding: BASE64 Content-ID: <20000101051236.L4587@patrocles.silby.com> Content-Description: Content-Disposition: ATTACHMENT; FILENAME="if_dc.diff" LS0tIGlmX2RjLmMub3JpZwlUaHUgT2N0IDExIDAxOjM5OjA1IDIwMDENCisr KyBpZl9kYy5jCVRodSBPY3QgMTEgMDE6Mzk6MzAgMjAwMQ0KQEAgLTE5Myw4 ICsxOTMsOCBAQA0KIHN0YXRpYyBpbnQgZGNfY29hbAkJX19QKChzdHJ1Y3Qg ZGNfc29mdGMgKiwgc3RydWN0IG1idWYgKiopKTsNCiBzdGF0aWMgdm9pZCBk Y19wbmljX3J4X2J1Z193YXIJX19QKChzdHJ1Y3QgZGNfc29mdGMgKiwgaW50 KSk7DQogc3RhdGljIGludCBkY19yeF9yZXN5bmMJCV9fUCgoc3RydWN0IGRj X3NvZnRjICopKTsNCi1zdGF0aWMgdm9pZCBkY19yeGVvZgkJX19QKChzdHJ1 Y3QgZGNfc29mdGMgKikpOw0KLXN0YXRpYyB2b2lkIGRjX3R4ZW9mCQlfX1Ao KHN0cnVjdCBkY19zb2Z0YyAqKSk7DQorc3RhdGljIGludCBkY19yeGVvZiAg ICAgICAgICAgX19QKChzdHJ1Y3QgZGNfc29mdGMgKikpOw0KK3N0YXRpYyBp bnQgZGNfdHhlb2YgICAgICAgICAgIF9fUCgoc3RydWN0IGRjX3NvZnRjICop 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