Hide Forgot
I've got a server with 3ware RAID card and a recent RHEL kernel on it. I've tried to update RAID firmware, but getting same slowness. Here's how you reproduce it: 1. open 2 shells 2. dd reading from device in first shell 3. do some I/O in second shell. 4. change scheduler to "deadline". Repeat 1-3, notice the huge difference. The kernel version is: 2.6.18-238.1.1.el5 Here are the results of tests: ========================================================= freshly booted machine <<launch dd in 1st shell>> [root@r1d1-28 ~]# cat /sys/block/sda/queue/scheduler noop anticipatory deadline [cfq] [root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null Warning: No matches found for: sadfaserZ real 0m24.948s user 0m0.344s sys 0m0.121s <<stop dd in 1st shell>> [root@r1d1-28 ~]# echo 0 > /sys/block/sda/queue/iosched/slice_idle [root@r1d1-28 ~]# echo 1 | tee /proc/sys/vm/drop_caches 1 <<launch dd in 1st shell>> [root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null Warning: No matches found for: sadfaserZ real 0m3.178s user 0m0.368s sys 0m0.136s <<stop dd in 1st shell>> [root@r1d1-28 ~]# echo deadline > /sys/block/sda/queue/scheduler [root@r1d1-28 ~]# echo 1 | tee /proc/sys/vm/drop_caches 1 <<launch dd in 1st shell>> [root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null Warning: No matches found for: sadfaserZ real 0m2.936s user 0m0.348s sys 0m0.131s ========================================================= I used "yum" because it does db-like i/o, but it doesn't matter - it could be anything requesting disk access. What would you recommend in this situation? I thought CFQ was fixed previous year in -192. Thanks!
Hi Yuri, Can you please open a ticket through Red Hat support if you have a subscription? Red Hat bugzilla is not meant as the first line of customer support, thanks!
I can't. I don't have a subscription. The same is observed with latest centos 5.5 kernel. The problem seems to be limited to this particular server, although I've tested only other two. Will get back once I have more info. But again, it happens only with CFQ, see my "test output".
Hi Yuri, If you don't have a subscription, the best way to get help is to post things to the upstream mailing list (for CFQ issues, Jens Axboe is the upstream lead and the right list is probably linux-kernel.org). Thanks!
This bug/component is not included in scope for RHEL-5.11.0 which is the last RHEL5 minor release. This Bugzilla will soon be CLOSED as WONTFIX (at the end of RHEL5.11 development phase (Apr 22, 2014)). Please contact your account manager or support representative in case you need to escalate this bug.
Thank you for submitting this request for inclusion in Red Hat Enterprise Linux 5. We've carefully evaluated the request, but are unable to include it in RHEL5 stream. If the issue is critical for your business, please provide additional business justification through the appropriate support channels (https://access.redhat.com/site/support).