Bug 276581 - Slowness with Qlogic HCAs
Slowness with Qlogic HCAs
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: openib (Show other bugs)
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medium Severity low
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Assigned To: Doug Ledford
Depends On:
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Reported: 2007-09-04 12:09 EDT by Gurhan Ozen
Modified: 2013-11-03 20:33 EST (History)
1 user (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2007-09-04 15:05:22 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Gurhan Ozen 2007-09-04 12:09:53 EDT
Description of problem:
This could be particular to low memory boxes , less than 4gb memory maybe? I
have the following message and a noticable slowness on the machines with Qlogic
cards on the boxes with 2GB of memory:

Sep  4 06:35:07 dell-pe1950-03 kernel: mtrr: base or size exceeds the MTRR width
Sep  4 06:35:07 dell-pe1950-03 kernel: ib_ipath 0000:0c:00.0: mtrr_add()  WC for
PIO bufs failed (-22)
Sep  4 06:35:07 dell-pe1950-03 kernel: ib_ipath 0000:0c:00.0: infinipath0: Write
combining not enabled (err 22): performance may be poor

The performance is indeed poor...

Compare this MT based client results:
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[  3] local port 39665 connected with port 5001
[  3]  0.0-10.0 sec  2.34 GBytes  2.01 Gbits/sec

To this IPATH based client results where the above errors are retrieved:

Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[  3] local port 59478 connected with port 5001
[  3]  0.0-10.0 sec    355 MBytes    297 Mbits/sec

Version-Release number of selected component (if applicable):
# uname -a
Linux dell-pe1950-02.rhts.boston.redhat.com 2.6.21-37.el5rt #1 SMP PREEMPT RT
Thu Aug 30 16:05:41 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux

How reproducible:

Steps to Reproduce:
1. Install an ipath based card on a box with less than 4 gb memory.
Actual results:

Expected results:

Additional info:
Comment 1 Doug Ledford 2007-09-04 15:05:22 EDT
MTRR stands for memory type range register.  It is the kernel provided means by
which you can configure the motherboard and CPU to do either caching, no
caching, or write combining on memory ranges.  The error in question means that
the ipath driver is attempting to use the general kernel facility for setting
the memory type of the IO memory on the card.  The CPU in the machine is not
allowing the memory type to be set to write combining.  Since the ipath cards
are mostly software driver based with the driver writing instructions into the
cards memory region, it goes much faster when multiple 32bit IO writes are
combined into a 32byte burst.  This doesn't happen on this machine because the
chipset isn't allowing that memory region to be mapped as write combining.  All
this really means is that the test machine you are using isn't well suited to
this card because the motherboard doesn't support what the card needs in order
to perform well (and it has nothing to do with RAM size, just motherboard memory
mapping capabilities).

Closing as NOTABUG.

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