I recently discovered why my new Gentoo server slows to a crawl on a intermediate load. The 2.6 kernel series is generating an unusual amount of iowait on my systems (reproducible on two systems with a KT400 and Sis735 chipset). iostat -c 1 while running something like bonnie produces iowaits of 99%. My workstation is only slightly less affected (up to 80%). Any 2.6 kernel responds the same (regardless of the patchset), even vanilla. 2.4 is fine (0% iowait) This is a sample iostat output -- avg-cpu: %user %nice %sys %iowait %idle 26.73 0.00 10.89 62.38 0.00 avg-cpu: %user %nice %sys %iowait %idle 0.00 0.00 13.00 87.00 0.00 avg-cpu: %user %nice %sys %iowait %idle 1.01 0.00 16.16 82.83 0.00 avg-cpu: %user %nice %sys %iowait %idle 0.00 0.00 11.88 88.12 0.00 avg-cpu: %user %nice %sys %iowait %idle 0.00 0.00 1.01 98.99 0.00 avg-cpu: %user %nice %sys %iowait %idle 0.99 0.00 2.97 96.04 0.00 -- I reported the bug at kernel.org http://bugzilla.kernel.org/show_bug.cgi?id=2864 Reproducible: Always Steps to Reproduce: 1. Install a 2.6 kernel 2. Run iostat -c 1, run something like bonnie (or cp, ...) 3. watch iowaits rise to 99% Actual Results: iowaits hang the system Expected Results: normal levels of iowait (equal to 2.4)
This is a upstream bug, thanks for filing it there.
