Hi John,
John L Griffin wrote:
My quick perusal of the current xeno-unstable code suggests that this
SCHED_OP call is a null call. The SCHED_OP macro attempts to call the
"do_block" function pointed to in the "struct scheduler sched_bvt_def"
array, but this function pointer is never initialized, so it just does a
NOP.
Yes. I agree.
It appears that what your patch does is limit when cpu_time gets updated,
such that the time only gets updated when the exec_domain is in the
BLOCKED state:
No. Currently, cpu_time will always get updated for the prev domain
when __enter_scheduler() is called. My patch modifies that behavior the
behavior so that it only gets updated if prev->blocked is false or if
prev->blocked is true but there are events pending for the domain. The
last part may not be right.
if ( test_bit(EDF_BLOCKED, &prev->ed_flags) )
prev->cpu_time += now - prev->lastschd;
}
Sorry, this is my fault, my mail client badly munged the patch when I
copy-pasted it. Let me show you the code:
if ( test_bit(EDF_BLOCKED, &prev->ed_flags) )
{
/* This check is needed to avoid a race condition. */
if ( event_pending(prev) )
clear_bit(EDF_BLOCKED, &prev->ed_flags);
else
SCHED_OP(do_block, prev);
}
prev->cpu_time += now - prev->lastschd;
Was changed to:
if ( test_bit(EDF_BLOCKED, &prev->ed_flags) )
{
/* This check is needed to avoid a race condition. */
if ( event_pending(prev) )
{
clear_bit(EDF_BLOCKED, &prev->ed_flags);
prev->cpu_time += now - prev->lastschd;
} else
SCHED_OP(do_block, prev);
} else {
prev->cpu_time += now - prev->lastschd;
}
It's not pretty at all. I'm not sure if the update after clear_bit() is
necessary either.
What this seems to be saying (in regard to your patch working) is that the
cpu_time is updated when the domain relinquishes the CPU by block()ing,
but cpu_time doesn't get updated if it relinquishes the CPU by yield()ing.
No, it's the opposite. Sorry, I think the whitespace munging made the
patch confusing.
I wonder why this works. Is anyone familiar with block() vs yield(), that
could lend some insight into what's going on?
I'm quite confident this is the cause of the problem. I'm just not sure
about that one cpu_time update.
Regards,
Anthony Liguori
JLG
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