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Third stage of unbreaking printing of pseudo-nice values (realtime

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priorities, etc.) in the NICE field:

Use a combination of pri_native and pri_user instead of pri_level to
guess the original realtime priority.  Using pri_level here has been
wrong since 2001/02/12.  Using only pri_native here would be correct
if the kernel actually initialized it reasonably.  (The kernel exports
its raw td_base_priority as pri_native, but userland mostly wants a
refined base priority).  Give up on waiting pri_native to work correctly
and only use it when there is nothing better (for kthreads).

This should reduce printing of bizarre pseudo-nice values.  Bizarre
values are still printed if we observe a transient borrowed priority
for a kthread (transient borrowing is the main thing that makes the
raw td_base_priority almost useless in userland), or if there is a
kernel bug.  One current kernel bug involves the kernel idprio thread
pagezero permanently changing its priority from PRI_MAX_IDLE (255) to
PUSER (160).  Then the bizarre value "ki-6" is printed instead of
"ki31".  Here "-6" is PRI_MIN_IDLE - PUSER = -64 truncated to 2
characters.  We are observing a transient borrowed priority that has
become permanent due to a bug.

ps/print.c:priorityr() needs similar changes (including ones in stage 2
here).
This commit is contained in:
Bruce Evans 2007-06-15 12:03:07 +00:00
parent 553284d74a
commit e19249f7a7
1 changed files with 25 additions and 2 deletions
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27
usr.bin/top/machine.c
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@ -892,7 +892,28 @@ format_nice(const struct kinfo_proc *pp)
case PRI_ITHD:
return ("-");
case PRI_REALTIME:
rtpri = pp->ki_pri.pri_level - PRI_MIN_REALTIME;
/*
* XXX: the kernel doesn't tell us the original rtprio and
* doesn't really know what it was, so to recover it we
* must be more chummy with the implementation than the
* implementation is with itself. pri_user gives a
* constant "base" priority, but is only initialized
* properly for user threads. pri_native gives what the
* kernel calls the "base" priority, but it isn't constant
* since it is changed by priority propagation. pri_native
* also isn't properly initialized for all threads, but it
* is properly initialized for kernel realtime and idletime
* threads. Thus we use pri_user for the base priority of
* user threads (it is always correct) and pri_native for
* the base priority of kernel realtime and idletime threads
* (there is nothing better, and it is usually correct).
*
* The field width and thus the buffer are too small for
* values like "kr31F", but such values shouldn't occur,
* and if they do then the tailing "F" is not displayed.
*/
rtpri = ((pp->ki_flag & P_KTHREAD) ? pp->ki_pri.pri_native :
pp->ki_pri.pri_user) - PRI_MIN_REALTIME;
snprintf(nicebuf, sizeof(nicebuf), "%sr%d%s",
kthread, rtpri, fifo);
break;
@ -902,7 +923,9 @@ format_nice(const struct kinfo_proc *pp)
snprintf(nicebuf, sizeof(nicebuf), "%d", pp->ki_nice - NZERO);
break;
case PRI_IDLE:
rtpri = pp->ki_pri.pri_level - PRI_MIN_IDLE;
/* XXX: as above. */
rtpri = ((pp->ki_flag & P_KTHREAD) ? pp->ki_pri.pri_native :
pp->ki_pri.pri_user) - PRI_MIN_IDLE;
snprintf(nicebuf, sizeof(nicebuf), "%si%d%s",
kthread, rtpri, fifo);
break;