Description of problem: When two or more O_DIRECT reads simultaneously run on different partitions of a disk, each performance critically slows down. An example of using multiple dd commands: # dd if=/dev/sdb1 of=/dev/null iflag=direct & # dd if=/dev/sdb2 of=/dev/null iflag=direct & The result of read performance is as follows: | number of dds | | 1 | 2 | 4 | -------------+-------+-------+-------| RHEL5.5 beta | 107.6 | 3.7 | 3.7 | RHEL5.4 | 109.1 | 78.1 | 75.0 | read speed (MB/s) We investigated this problem and found the patch causing this problem. linux-2.6-block-cfq-iosched-fix-idling-interfering-with-plugging.patch When we removed this patch from 5.5 beta, this problem did not occur. It is a critical performance regression. So, we can not ship the RHEL5.5 until this problem is fixed. Version-Release number of selected component (if applicable): 2.6.18-187.el5 How reproducible: 100% The fix is already upstream, and was tested by the customer: commit 2d870722965211de072bb36b446a4df99dae07e1
This request was evaluated by Red Hat Product Management for inclusion in a Red Hat Enterprise Linux maintenance release. Product Management has requested further review of this request by Red Hat Engineering, for potential inclusion in a Red Hat Enterprise Linux Update release for currently deployed products. This request is not yet committed for inclusion in an Update release.
in kernel-2.6.18-192.el5 You can download this test kernel from http://people.redhat.com/jwilson/el5 Please update the appropriate value in the Verified field (cf_verified) to indicate this fix has been successfully verified. Include a comment with verification details.
*** Bug 574285 has been marked as a duplicate of this bug. ***
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2010-0178.html