From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: From: erik quanstrom Date: Wed, 13 May 2009 08:34:10 -0400 To: 9fans@9fans.net In-Reply-To: <816fc530f45f9acd7946837e73cef773@quintile.net> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: Re: [9fans] cfs Topicbox-Message-UUID: f9835046-ead4-11e9-9d60-3106f5b1d025 > Why is cfs in the kernel and not a userlevel program? i don't know. but by putting cfs in the kernel, you can use the kernel's built-in concurrency. cfs predates the thread library. > I guess there might be performance issues also, though these would > be swamped by the performance improvment of plugging in CFS in the > first place (IMHO). why guess? we can get a good approximation. the difference is a round trip to user space which has bandwidth and latency costs. i used dd and ramfs to simulate. userspace kernel b/w latency b/w latency i7 2666 460 MB/s 1680µs 3900 MB/s 118µs Xeon5000 1859 156 MB/s 1205 868 265 AMD64 2604 be 142 MB/s 2511µs 2600 332 AMD64 2004 135 MB/s 2510 2600 324 if you're limited by 1gbe, the bandwidth would be good but the latency is spoiled. if you're limited by 10gbe, the vodka's weak, too. - erik