Do_ade

Do_ade

[hermit]

We are trying to run WEBkit on MIPS 24ke system.
we found a lot of "do_ade" print. but system doesn't crash. 
because of do_ade print, the system performance seems poor.
I wonder if there is any compile flag can remove do_ade warning?
Thanks!
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Re: Do_ade

[David VomLehn]

On Mon, Dec 21, 2009 at 02:47:22AM -0600, hermit wrote:
> 
> We are trying to run WEBkit on MIPS 24ke system.
> we found a lot of "do_ade" print. but system doesn't crash. 
> because of do_ade print, the system performance seems poor.
> I wonder if there is any compile flag can remove do_ade warning?
> Thanks!
> -- 
> View this message in context: http://old.nabble.com/Do_ade-tp26871250p26871250.html
> Sent from the linux-mips main mailing list archive at Nabble.com.
> 
> 

If you get messages from do_ade(), it means that your application is
accessing data that is not aligned on a boundary that is a multiple
of the size of the data. Accessing such unaligned data causes an exception
that one would typically expect to kill your process. Fortunately, or
unfortunately, depending on your view, the code that handles this exception
can be configured to do one of three things:

o	Send a SIGBUS signal to your process, which generally kills it
o	Print a message and then emulate the unaligned load or store
o	Silently emulate the unaligned load or store

It sounds like your system is configured for the print and emulate option.
The emulation is quite a bit slower than a simple aligned load or store,
so I am not surprised you are seeing noticable performance impact. The warning
may be impacting your performance as it is printed sychronously, but even
if you silence the warning, your performance will suffer.

There are various ways that you can get unaligned accesses. One is to have
code that does bad pointer arithmetic. Another possiblity, one that I
encountered recently, is to have a bad gcc. IIRC gcc 4.1.0 had this problem.
Upgrading the version of gcc caused the problem to go away, but it wasn't
really clear what bug fix did the job. Anyway, I know that verson 4.3.2
works as you would expect.

I strongly recommend, if you have an older gcc, that you upgrade. An
instruction emulated through exception handling can easily be a hundred times
slower than that instruction operating on aligned data. If, however, you
really only want to quiet the warning, you must first mount the debugfs
filesystem: "mount -t debugfs debug /proc/sys/debug". Then write a zero to
/proc/sys/debug/mips/unaligned_action, i.e.
echo 0 >/proc/sys/debug/mips/unaligned_action.

-- 
David VL

Re: Do_ade

[hermit]

David
       Thanks!
       My GCC version is 4.2.3. it seems that it is not too old. I believe
there is bad pointer arithmetic. 
       Here is the do_ade print:
       do_ade, 542 address error exception occurs! MediaPlayerServ(pid:839)
        (a0 == 7edff5b6 a1 == 302daaca a2 == 00000002 a3 == 302daaca)
        (gp == 302e2730 sp == 7edff578 t9 == 2afb4640)
        (epc == 302c3250, ra == 302c3388)
        Suppose we can find which function cause "bad pointer arithmetic". 
        I am new to MIPS, anybody can tell me how i can find the function?
        Thanks!
BGs/Hermit

David VomLehn (dvomlehn) wrote:
> 
> On Mon, Dec 21, 2009 at 02:47:22AM -0600, hermit wrote:
>> 
>> We are trying to run WEBkit on MIPS 24ke system.
>> we found a lot of "do_ade" print. but system doesn't crash. 
>> because of do_ade print, the system performance seems poor.
>> I wonder if there is any compile flag can remove do_ade warning?
>> Thanks!
>> -- 
>> View this message in context:
>> http://old.nabble.com/Do_ade-tp26871250p26871250.html
>> Sent from the linux-mips main mailing list archive at Nabble.com.
>> 
>> 
> 
> If you get messages from do_ade(), it means that your application is
> accessing data that is not aligned on a boundary that is a multiple
> of the size of the data. Accessing such unaligned data causes an exception
> that one would typically expect to kill your process. Fortunately, or
> unfortunately, depending on your view, the code that handles this
> exception
> can be configured to do one of three things:
> 
> o	Send a SIGBUS signal to your process, which generally kills it
> o	Print a message and then emulate the unaligned load or store
> o	Silently emulate the unaligned load or store
> 
> It sounds like your system is configured for the print and emulate option.
> The emulation is quite a bit slower than a simple aligned load or store,
> so I am not surprised you are seeing noticable performance impact. The
> warning
> may be impacting your performance as it is printed sychronously, but even
> if you silence the warning, your performance will suffer.
> 
> There are various ways that you can get unaligned accesses. One is to have
> code that does bad pointer arithmetic. Another possiblity, one that I
> encountered recently, is to have a bad gcc. IIRC gcc 4.1.0 had this
> problem.
> Upgrading the version of gcc caused the problem to go away, but it wasn't
> really clear what bug fix did the job. Anyway, I know that verson 4.3.2
> works as you would expect.
> 
> I strongly recommend, if you have an older gcc, that you upgrade. An
> instruction emulated through exception handling can easily be a hundred
> times
> slower than that instruction operating on aligned data. If, however, you
> really only want to quiet the warning, you must first mount the debugfs
> filesystem: "mount -t debugfs debug /proc/sys/debug". Then write a zero to
> /proc/sys/debug/mips/unaligned_action, i.e.
> echo 0 >/proc/sys/debug/mips/unaligned_action.
> 
> -- 
> David VL
> 
> 
> 

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Re: Do_ade

[Ralf Baechle]

On Wed, Dec 23, 2009 at 02:42:48AM -0800, hermit wrote:

>        My GCC version is 4.2.3. it seems that it is not too old. I believe
> there is bad pointer arithmetic. 
>        Here is the do_ade print:
>        do_ade, 542 address error exception occurs! MediaPlayerServ(pid:839)
>         (a0 == 7edff5b6 a1 == 302daaca a2 == 00000002 a3 == 302daaca)
>         (gp == 302e2730 sp == 7edff578 t9 == 2afb4640)
>         (epc == 302c3250, ra == 302c3388)
>         Suppose we can find which function cause "bad pointer arithmetic". 
>         I am new to MIPS, anybody can tell me how i can find the function?
>         Thanks!

This is not the normal kernel printout.  It would seem that somebody who
didn't know about the existence of the logging code added this code.  The
number 542 presumably is a line number and do_ade is in
arch/mips/kernel/unaligned.c.  So look around line 542 in that file.

  Ralf

Re: Do_ade

[David VomLehn]

On Wed, Dec 23, 2009 at 06:40:29AM -0600, Ralf Baechle wrote:
> On Wed, Dec 23, 2009 at 02:42:48AM -0800, hermit wrote:
> 
> >        My GCC version is 4.2.3. it seems that it is not too old. I believe
> > there is bad pointer arithmetic. 
> >        Here is the do_ade print:
> >        do_ade, 542 address error exception occurs! MediaPlayerServ(pid:839)
> >         (a0 == 7edff5b6 a1 == 302daaca a2 == 00000002 a3 == 302daaca)
> >         (gp == 302e2730 sp == 7edff578 t9 == 2afb4640)
> >         (epc == 302c3250, ra == 302c3388)
> >         Suppose we can find which function cause "bad pointer arithmetic". 
> >         I am new to MIPS, anybody can tell me how i can find the function?
> >         Thanks!
> 
> This is not the normal kernel printout.  It would seem that somebody who
> didn't know about the existence of the logging code added this code.  The
> number 542 presumably is a line number and do_ade is in
> arch/mips/kernel/unaligned.c.  So look around line 542 in that file.

If I understand hermit's problem, knowing the line in unaligned.c won't
help much since the problem appears to be in the application MediaPayerServ.
My suggestion is to use addr2line on the location where the exception
occurred, which is the EPC value 302c3250. The addr2line utility can be used
on the unstripped version of the userspace executable to determine the
function, file, and line number where the unaligned access was made.

>   Ralf

-- 
David VL