On Mon, 29 Sep 2014 09:28:37 -0400 (EDT) Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 28 Sep 2014, Mark Knibbs wrote: > > > > There's no telling the reason for this difference. It's got to be a > > > hardware issue, though, not a software problem. Maybe your xHCI > > > controller just isn't optimized for carrying out full-speed transfers. > > > > That's a possibility, but the improvement between my initial test with > > kernel 3.14 and 3.16.2 (0.63MB/sec -> 0.75MB/sec) was obviously down to > > software. > > Since you reliably observe a difference in speed between these kernels, > you are in an ideal situation to use bisection. That ought to pinpoint > the code changes responsible for the speed difference. I finally finished doing git bisect between 2.6.33 and 2.6.34. Sadly I'm not really any the wiser, since the result looks pretty bogus. The supposedly-bad commit was: 002345925e6c45861f60db6f4fc6236713fd8847 syslog: distinguish between /proc/kmsg and syscalls There doesn't seem to be anything in that which could cause the problem; perhaps something went wrong with the bisection? That commit doesn't cleanly revert with later kernel versions. At this point I'm pretty much stumped. Each kernel version seemed consistently "good" or "bad". I tested 2.6.33.20 five times, rebooting and/or power-cycling between tests, and in every case the USB3 rate was 100.05% or 100.06% times the USB2 rate. All "good" kernels in the bisection were like that. Some "bad" kernels did show widely varying results, but all were noticeably lower than the good case. For example, the results I got for testing 2.6.34.7 five times (USB3 speed as percentage of USB2 speed): 98.72%, 90.66%, 90.90%, 82.18%, 71.28% And testing 2.6.34.4: 65.69%, 65.60%, 71.77% In case it's of any use, here's the output of git bisect log I got. git bisect start # good: [60b341b778cc2929df16c0a504c91621b3c6a4ad] Linux 2.6.33 git bisect good 60b341b778cc2929df16c0a504c91621b3c6a4ad # bad: [e40152ee1e1c7a63f4777791863215e3faa37a86] Linus 2.6.34 git bisect bad e40152ee1e1c7a63f4777791863215e3faa37a86 # bad: [64ba9926759792cf7b95f823402e2781edd1b5d4] Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd git bisect bad 64ba9926759792cf7b95f823402e2781edd1b5d4 # good: [d3ae8562d43fe2b97d605dd67dc67bf8fa9b956a] usb: host: ehci: fix missing kfree in remove path also git bisect good d3ae8562d43fe2b97d605dd67dc67bf8fa9b956a # good: [2ac2ed5f2dfc97ae9ed9f446ad6e064fa821ef6d] gigaset: small documentation improvement git bisect good 2ac2ed5f2dfc97ae9ed9f446ad6e064fa821ef6d # bad: [c1dcb4bb1e3e16e9baee578d9bb040e5fba1063e] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394-2.6 git bisect bad c1dcb4bb1e3e16e9baee578d9bb040e5fba1063e # good: [5057bfaff82e12f01a2ffd58f55535cbd7c5c3a2] Merge branch 'omap-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap-2.6 git bisect good 5057bfaff82e12f01a2ffd58f55535cbd7c5c3a2 # bad: [3ff1562ea48cddaa5ac1adcb8892227389a4c96c] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/roland/infiniband git bisect bad 3ff1562ea48cddaa5ac1adcb8892227389a4c96c # bad: [832d30ca72c0a59058e66e097f5ea11f99640819] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6 git bisect bad 832d30ca72c0a59058e66e097f5ea11f99640819 # good: [d2e82add832f9c95376d004d565c5e164c99b9ec] OMAP: DSS2: OMAPFB: install omapfb.h git bisect good d2e82add832f9c95376d004d565c5e164c99b9ec # bad: [d78ca3cd733d8a2c3dcd88471beb1a15d973eed8] syslog: use defined constants instead of raw numbers git bisect bad d78ca3cd733d8a2c3dcd88471beb1a15d973eed8 # good: [e41035a996356c257183e53a70abfb46fa84908b] TOMOYO: Remove memory pool for string data. git bisect good e41035a996356c257183e53a70abfb46fa84908b Mark -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
