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On 04/04/2011 05:52 PM, Charles G Waldman wrote: > > > Are any of xrootd team aware of > > http://twiki.mwt2.org/bin/view/ITB/UltraLightKernel ? are there any (up > > to date) recommendations based on this guys work? > > Hi - Hi! > I'm involved with both xrootd and the configuration of the Ultralight > kernel. great! you guys do an superb job (as far i seen in graphs :) ) > The major difference between the UltraLight kernel and the stock SL > kernel is that the SL kernel is configured with preemption enabled, > which is great for a user desktop, but not for a high-throughput > data server. and is this the only difference? > We have found that on our test server (16-core server Dell 2950 with 6 > RAID6 shelves) with the SL kernel, under load, the "ksoftirqd" daemon so the speed benchmark is done accessing all 6 raid6 arrays or just one raid? > takes up 100% CPU (this is a kernel thread involved in preemption), > and the xrootd process is only able to deliver data at about 500MB/sec > (about 50% of theoretical max on a on a 10Gb link). > > With the UL kernel, the "ksoftirq" CPU usage goes away completely, and > xrootd is easily able to deliver data at wire speed (~1000MB/sc) great news!!! Thanks a lot! Adrian > > - Charles