Enhancements in Linux kernel 2.6.13 and possibility to backport

Martin Holt Juliussen mjuliuss at online.no
Tue Sep 20 13:23:32 CDT 2005

On Tue, 2005-09-20 at 13:48 +0100, Matthew Garrett wrote:
> On Tue, Sep 20, 2005 at 02:12:55PM +0200, Martin Holt Juliussen wrote:
> > The reason why I'm not filing this as a bug report is that I think it
> > should be discussed if those patches used to fix those issues should be
> > backported to 2.6.12 used in breezy, so it is possible to use stock
> > Ubuntu kernel even if you got a orionoco based wlan card or if you got
> > problems with the USB at startup. If they aren't the fixes will not be
> > included before breezy +1 I assume.
> If you can identify the fixes for the USB issue, then they may be 
> included. It's unlikely that driver updates will be made now.

It might be this (taken from the 2.6.13 changelog):

        commit 8a9e1b0f564615bd92ba50162623e25c2904e564
        Author: Venkatesh Pallipadi <venkatesh.pallipadi at intel.com>
        Date:   Thu Jun 23 00:08:13 2005 -0700
            [PATCH] Platform SMIs and their interferance with tsc based delay calibration
            Current tsc based delay_calibration can result in significant errors in
            loops_per_jiffy count when the platform events like SMIs
            (System Management Interrupts that are non-maskable) are present. This could
            lead to potential kernel panic(). This issue is becoming more visible with 2.6
            kernel (as default HZ is 1000) and on platforms with higher SMI handling
            latencies. During the boot time, SMIs are mostly used by BIOS (for things
            like legacy keyboard emulation).
            The psuedocode for current delay calibration with tsc based delay looks like
            (0) Estimate a value for loops_per_jiffy
            (1) While (loops_per_jiffy estimate is accurate enough)
            (2)   wait for jiffy transition (jiffy1)
            (3)   Note down current tsc (tsc1)
            (4)   loop until tsc becomes tsc1 + loops_per_jiffy
            (5)   check whether jiffy changed since jiffy1 or not and refine
            loops_per_jiffy estimate
            Consider the following cases
            Case 1:
            If SMIs happen between (2) and (3) above, we can end up with a
            loops_per_jiffy value that is too low. This results in shorted delays and
            kernel can panic () during boot (Mostly at IOAPIC timer initialization
            timer_irq_works() as we don't have enough timer interrupts in a specified
            Case 2:
            If SMIs happen between (3) and (4) above, then we can end up with a
            loops_per_jiffy value that is too high. And with current i386 code, too
            high lpj value (greater than 17M) can result in a overflow in
            delay.c:__const_udelay() again resulting in shorter delay and panic().
            The patch below makes the calibration routine aware of asynchronous events
            like SMIs. We increase the delay calibration time and also identify any
            significant errors (greater than 12.5%) in the calibration and notify it to
            Patch below changes both i386 and x86-64 architectures to use this
            new and improved calibrate_delay_direct() routine.
            Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi at intel.com>
            Signed-off-by: Adrian Bunk <bunk at stusta.de>
            Signed-off-by: Andrew Morton <akpm at osdl.org>
            Signed-off-by: Linus Torvalds <torvalds at osdl.org>

Martin Holt Juliussen <mjuliuss at online.no>

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