From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051018 Epiphany/1.8.2 Description of problem: After upgrading the SMP kernel on my PR440FX box, the SCSI subsystem switched from U-SCSI to FAST-SCSI mode. There are three devices connected to the on-board AHA-2940UW device. This never happened before up to revision 2.6.12-1.1447_FC4. The relevant section of the "dmesg" log message looks quite different now. Some major changes related to the SCSI system seem to have happened between kernel version 2.6.12 and 2.6.13. Version-Release number of selected component (if applicable): kernel-smp-2.6.13-1.1526_FC4 How reproducible: Always Steps to Reproduce: 1. Boot with 2.6.13-1.1526_FC4 SMP kernel. 2. Check the output of "dmesg". Actual Results: Transfer mode should be U-SCSI (20 MB/s) as before. Expected Results: Transfer mode is FAST-SCSI (10 MB/s). Additional info: The hard disk transfer drops from about 28 MB/s to a disappointing 18 MB/s whereby the latter is obvious having in mind that the disk operates in "wide" mode. The upper limit hence is 20 MB/s. Booting the 2.6.12-1.1447_FC4 kernel restores the U-SCSI mode. Consequently, it is not a matter of BIOS settings etc.
Ok, the SCSI-subsystem is indeed identical (v6.2.36). Looking at the content of "/var/log/dmesg" though reveals that for the latest kernel, *asynchronous* transfer mode is adopted which explains the limits of 10 MB/s for 8-Bit and 20 MB/s for 16-Bit devices. The attached hard disk is a QUANTUM Atlas 10k III drive.
Created attachment 120298 [details] SCSI portion of "dmesg" for 2.6.12-1.1447_FC4smp kernel
Created attachment 120299 [details] SCSI portion of "dmesg" for 2.6.13-1.1532_FC4smp kernel
I verified my observation by installing an AHA-2940U2W PCI card. The "dmesg" log looks pretty much like the previous one for the on-board AIC7880 chip. Even the "asynchronous" message is issued. However, transfer mode now is FAST-40 SCSI compared to FAST-10 mode for the AIC7880 chip. This gives a factor of 4 where it should only be 2. Looks like a problem specifically related to to the AIC7880. In both cases, I had disconnected any drive except for the QUANTUM Atlas 10k III.
2.6.14-1.1637_FC4 has been released as an update for FC4. Please retest with this update, as a large amount of code has been changed in this release, which may have fixed your problem. Thank you.
Still not fixed in 2.6.14-1.1740_FC5smp. As before, I disconnected any other device but the U160 hard disk before booting. The kernel continues to negotiate FAST-10 WIDE mode which limits data transfers to 20 MB/s. In practice, I obtain about 18 MB/s.
Created attachment 122030 [details] SCSI portion of "dmesg" for 2.6.14-1.1740_FC5smp kernel
Still not fixed in 2.6.15-1.1881_FC5smp.
This is a mass-update to all currently open kernel bugs. A new kernel update has been released (Version: 2.6.15-1.1830_FC4) based upon a new upstream kernel release. Please retest against this new kernel, as a large number of patches go into each upstream release, possibly including changes that may address this problem. This bug has been placed in NEEDINFO_REPORTER state. Due to the large volume of inactive bugs in bugzilla, if this bug is still in this state in two weeks time, it will be closed. Should this bug still be relevant after this period, the reporter can reopen the bug at any time. Any other users on the Cc: list of this bug can request that the bug be reopened by adding a comment to the bug. If this bug is a problem preventing you from installing the release this version is filed against, please see bug 169613. Thank you.
I had already moved to FC5-rawhide some time ago where the problem is also present, e.g. for kernel version 2.6.15-1.1885_FC5smp.
Still not fixed in 2.6.15-1.1831_FC4smp either.
Still not fixed in 2.6.15-1.1969_FC5smp.
In the meantime, another user has posted a bug report upstream for this issue, see: http://bugzilla.kernel.org/show_bug.cgi?id=5808
Still not fixed in 2.6.15-1.2032_FC5smp.
Still present in both 2.6.15-1.2096_FC5smp and 2.6.16-1.2147_FC6. Very annoying!
The first is one is 2.6.16-1.2096_FC5smp, sorry. ^^
Created attachment 133919 [details] SCSI portion of "dmesg" for 2.6.17-1.2532.fc6 SMP kernel
Kernel 2.6.17-1.2532.fc6 still negotiates "FAST-10 WIDE SCSI" mode when it should be "FAST-20 WIDE SCSI".
Still broken in kernel "2.6.19-1.2877.fc7".
Still broken in kernel "2.6.21-1.3194.fc7"
Still broken in kernel "2.6.23-0.45.rc0.git16.fc8".
There is some progress on this issue since by executing echo 50 > /sys/class/spi_transport/target0:0:0/min_period echo 1 > /sys/class/spi_transport/target0:0:0/revalidate the SCSI controller can be switched to ULTRA mode as reported by dmesg: target0:0:0: Beginning Domain Validation target0:0:0: asynchronous target0:0:0: wide asynchronous target0:0:0: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 8) target0:0:0: Domain Validation skipping write tests target0:0:0: Ending Domain Validation Transfer mode is reported as asynchronous but this seems to be ok. However, for development kernel version 2.6.23-0.49.rc1.git3.fc8, the improvement even in single user mode is small. One manages to achieve a transfer rate of about 20 MB/s instead of 18 MB/s. Only after booting the latest F7 update kernel 2.6.22.1-33.fc7, the transfer rate achieved a value of about 28 MB/s which seems reasonable for a U160 hard disk connected to a 2940UW controller in SE mode. Using a Ubuntu live CD where the hard disk is not at all used by the OS itself, I even obtained a rate of about 32 MB/s. It seems that the debug options of Fedora development kernels have a huge impact on SCSI performance which actually misled me for a while. To summarize: SCSI operations is correct after switching the mode to U-SCSI by hand. What thus merely needs to be fixed is the wrong negociation of FAST-10 instead of FAST-20 mode.
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Comment #23 still fully applies to current F9 w/updates plus kernel-2.6.26.1-9.fc9.i686. The issue thus persists.
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For current F13 including kernel-2.6.34.7-66.fc13.i686, min_period is still erroneously set to 100 ns instead of 50 ns. As measured by gnome-disk-utility, forcing a value of 50 ns for min_period following the procedure outlined in comment 23, the average read rate jumps from 18 MB/s to 34 MB/s.
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Issue still applies to F14 and the latest kernel-2.6.35.13-92.fc14.
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