The problem occurs when e.g. drivers use time_after(jiffes, timeout).
CONFIG_NO_HZ could make jiffies advance by more than 1.
This is done by: tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
If drivers use a timeout value of jiffies+1,
"time_after(jiffies, timeout)" will be true after 1 interrupt
(given that it advances jiffies by at least 2).
This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer
for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250, CONFIG_NO_HZ=y).
do_write_buffer does the following:
unsigned long uWriteTimeout = ( HZ / 1000 ) + 1;
...
timeo = jiffies + uWriteTimeout;
...
for (;;) {
...
if (time_after(jiffies, timeo) && !chip_ready(map, adr))
break;
if (chip_ready(map, adr)) {
xip_enable(map, chip, adr);
goto op_done;
}
UDELAY(map, chip, adr, 1);
}
/* software timeout */
ret = -EIO;
opdone:
...
I've seen a few software timeouts after the for-loop
looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically
our NOR flash (S29GL01GP) may need upto ~ 200 us to be ready.
disabling CONFIG_NO_HZ fixes the problem.
replacing time_after by a for-loop counter to loop max 1000 times
also fixes the problem.
the latest kernel seems to have the same problem.
do I miss something here or is this a known problem of CONFIG_NO_HZ ?
Is XIP enabled? It seems that the xip_udelay is not very accurate, and
may be the cause of what you are seeing.
On Thu, Sep 3, 2009 at 12:50 PM, Norbert van
Bolhuis<[email protected]> wrote:
>
> The problem occurs when e.g. drivers use time_after(jiffes, timeout).
>
> CONFIG_NO_HZ could make jiffies advance by more than 1.
> This is done by:
> tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
>
> If drivers use a timeout value of jiffies+1,
> "time_after(jiffies, timeout)" will be true after 1 interrupt
> (given that it advances jiffies by at least 2).
>
> This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer
> for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250, CONFIG_NO_HZ=y).
>
> do_write_buffer does the following:
> unsigned long uWriteTimeout = ( HZ / 1000 ) + 1;
> ...
> timeo = jiffies + uWriteTimeout;
> ...
> for (;;) {
> ...
> if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> break;
> if (chip_ready(map, adr)) {
> xip_enable(map, chip, adr);
> goto op_done;
> }
> UDELAY(map, chip, adr, 1);
> }
> /* software timeout */
> ret = -EIO;
> opdone:
> ...
>
> I've seen a few software timeouts after the for-loop
> looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically
> our NOR flash (S29GL01GP) may need upto ~ 200 us to be ready.
>
> disabling CONFIG_NO_HZ fixes the problem.
> replacing time_after by a for-loop counter to loop max 1000 times
> also fixes the problem.
>
> the latest kernel seems to have the same problem.
>
> do I miss something here or is this a known problem of CONFIG_NO_HZ ?
> --
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--
__________________________________________________________________________
dott. Corrado Zoccolo mailto:[email protected]
PhD - Department of Computer Science - University of Pisa, Italy
--------------------------------------------------------------------------
The self-confidence of a warrior is not the self-confidence of the average
man. The average man seeks certainty in the eyes of the onlooker and calls
that self-confidence. The warrior seeks impeccability in his own eyes and
calls that humbleness.
Tales of Power - C. Castaneda
Corrado Zoccolo wrote:
> Is XIP enabled? It seems that the xip_udelay is not very accurate, and
> may be the cause of what you are seeing.
>
no it isn't. CONFIG_MTD_XIP has been disabled.
nor did someone supsended the write (chip->state remains FL_WRITING).
Norbert van Bolhuis wrote:
>
> The problem occurs when e.g. drivers use time_after(jiffes, timeout).
>
> CONFIG_NO_HZ could make jiffies advance by more than 1.
> This is done by:
> tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
>
> If drivers use a timeout value of jiffies+1,
> "time_after(jiffies, timeout)" will be true after 1 interrupt
> (given that it advances jiffies by at least 2).
>
> This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer
> for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250,
> CONFIG_NO_HZ=y).
>
> do_write_buffer does the following:
> unsigned long uWriteTimeout = ( HZ / 1000 ) + 1;
> ...
> timeo = jiffies + uWriteTimeout;
> ...
> for (;;) {
> ...
> if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> break;
> if (chip_ready(map, adr)) {
> xip_enable(map, chip, adr);
> goto op_done;
> }
> UDELAY(map, chip, adr, 1);
> }
> /* software timeout */
> ret = -EIO;
> opdone:
> ...
>
> I've seen a few software timeouts after the for-loop
> looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically
Are you sure? UDELAY may call schedule(), which can return to this thread
after much longer time than 13us...
Marcin
On Thu 2009-09-03 12:50:12, Norbert van Bolhuis wrote:
>
> The problem occurs when e.g. drivers use time_after(jiffes, timeout).
>
> CONFIG_NO_HZ could make jiffies advance by more than 1.
> This is done by: tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
jiffies really should be up-to-date as long as you are running
anything else than idle loop. If not, that's a bug ... and nasty one.
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
On Sat 2009-09-05 20:19:46, Marcin Slusarz wrote:
> Norbert van Bolhuis wrote:
> >
> > The problem occurs when e.g. drivers use time_after(jiffes, timeout).
> >
> > CONFIG_NO_HZ could make jiffies advance by more than 1.
> > This is done by:
> > tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
> >
> > If drivers use a timeout value of jiffies+1,
> > "time_after(jiffies, timeout)" will be true after 1 interrupt
> > (given that it advances jiffies by at least 2).
> >
> > This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer
> > for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250,
> > CONFIG_NO_HZ=y).
> >
> > do_write_buffer does the following:
> > unsigned long uWriteTimeout = ( HZ / 1000 ) + 1;
> > ...
> > timeo = jiffies + uWriteTimeout;
> > ...
> > for (;;) {
> > ...
> > if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > break;
> > if (chip_ready(map, adr)) {
> > xip_enable(map, chip, adr);
> > goto op_done;
> > }
> > UDELAY(map, chip, adr, 1);
> > }
> > /* software timeout */
> > ret = -EIO;
> > opdone:
> > ...
> >
> > I've seen a few software timeouts after the for-loop
> > looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically
>
> Are you sure? UDELAY may call schedule(), which can return to this thread
> after much longer time than 13us...
Too long wait is expected, but AFAICS he's complaining about too short
delay and that's a hard bug.
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
Pavel Machek wrote:
> On Sat 2009-09-05 20:19:46, Marcin Slusarz wrote:
>> Norbert van Bolhuis wrote:
>>> The problem occurs when e.g. drivers use time_after(jiffes, timeout).
>>>
>>> CONFIG_NO_HZ could make jiffies advance by more than 1.
>>> This is done by:
>>> tick_nohz_update_jiffies->tick_do_update_jiffies64->do_timer
>>>
>>> If drivers use a timeout value of jiffies+1,
>>> "time_after(jiffies, timeout)" will be true after 1 interrupt
>>> (given that it advances jiffies by at least 2).
>>>
>>> This is exactly what happens in cfi_cmdset_0002.c:do_write_buffer
>>> for our case (Powerpc MPC8313, linux-2.6.28, CONFIG_HZ=250,
>>> CONFIG_NO_HZ=y).
>>>
>>> do_write_buffer does the following:
>>> unsigned long uWriteTimeout = ( HZ / 1000 ) + 1;
>>> ...
>>> timeo = jiffies + uWriteTimeout;
>>> ...
>>> for (;;) {
>>> ...
>>> if (time_after(jiffies, timeo) && !chip_ready(map, adr))
>>> break;
>>> if (chip_ready(map, adr)) {
>>> xip_enable(map, chip, adr);
>>> goto op_done;
>>> }
>>> UDELAY(map, chip, adr, 1);
>>> }
>>> /* software timeout */
>>> ret = -EIO;
>>> opdone:
>>> ...
>>>
>>> I've seen a few software timeouts after the for-loop
>>> looped only 13 times (= 13 us delay, i.s.o. the expected 1 ms). Typically
>> Are you sure? UDELAY may call schedule(), which can return to this thread
>> after much longer time than 13us...
>
> Too long wait is expected, but AFAICS he's complaining about too short
> delay and that's a hard bug.
Yeah, I know. But conclusion is a bit fishy - 13 iterations don't necessarily mean 13us.
Bug might be elsewhere.
Marcin