Hi Brian,
On Fri, May 24, 2024 at 12:08:28PM GMT, Brian Norris wrote:
> Utilization attributes were added in Linux v5.3 via commit a509a7cd7974
> ("sched/uclamp: Extend sched_setattr() to support utilization
> clamping"). Borrow some documentation from there, with a bit of
> editorial trimming and augmentation.
>
> The "reset" (-1 / UINT32_MAX) behavior was added in Linux 5.11 via
> commit 480a6ca2dc6e ("sched/uclamp: Allow to reset a task uclamp
> constraint value").
>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Patrick Bellasi <patrick.bellasi@xxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> ---
> man/man2/sched_setattr.2 | 65 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 63 insertions(+), 2 deletions(-)
>
> diff --git a/man/man2/sched_setattr.2 b/man/man2/sched_setattr.2
> index 5d7061bd6e3a..4b940d76de53 100644
> --- a/man/man2/sched_setattr.2
> +++ b/man/man2/sched_setattr.2
> @@ -94,10 +94,14 @@ .SS sched_setattr()
> SCHED_BATCH) */
> u32 sched_priority; /* Static priority (SCHED_FIFO,
> SCHED_RR) */
> - /* Remaining fields are for SCHED_DEADLINE */
> + /* For SCHED_DEADLINE */
LGTM.
> u64 sched_runtime;
> u64 sched_deadline;
> u64 sched_period;
> +
Please don't use blank lines in the source code. They trigger a
warning. For that, you can use the dummy escape sequence:
\&
> + /* Utilization hints */
> + u32 sched_util_min;
> + u32 sched_util_max;
LGTM.
> };
> .EE
> .in
> @@ -186,6 +190,20 @@ .SS sched_setattr()
> On the other hand, if the process-directed signal is delivered to
> a thread inside the process other than the one that had a run-time overrun,
> the application has no way of knowing which thread overran.
> +.TP
> +.BR SCHED_FLAG_UTIL_CLAMP_MIN ", " SCHED_FLAG_UTIL_CLAMP_MAX " (since Linux 5.3)"
I'd use separate tags, with TQ:
.TP
.B SCHED_FLAG_UTIL_CLAMP_MIN
.TQ
.BR SCHED_FLAG_UTIL_CLAMP_MAX " (both since Linux 5.3)"
> +These flags indicate that the
> +.I
> +sched_util_min
> +or
> +.I
> +sched_util_max
> +fields, respectively, are present, representing the expected minimum and
> +maximum utilization of the thread.
Please use semantic newlines.
$ MANWIDTH=72 man man-pages | sed -n '/Use semantic newlines/,/^$/p'
Use semantic newlines
In the source of a manual page, new sentences should be started on
new lines, long sentences should be split into lines at clause
breaks (commas, semicolons, colons, and so on), and long clauses
should be split at phrase boundaries. This convention, sometimes
known as "semantic newlines", makes it easier to see the effect of
patches, which often operate at the level of individual sentences,
clauses, or phrases.
> +.IP
> +The utilization attributes provide the scheduler with boundaries within which
> +it should schedule the thread, potentially informing its decisions regarding
> +task placement and frequency selection.
> .RE
> .TP
> .I sched_nice
> @@ -228,6 +246,33 @@ .SS sched_setattr()
> .I sched_period
> This field specifies the "Period" parameter for deadline scheduling.
> The value is expressed in nanoseconds.
> +.TP
> +.IR sched_util_min ", " sched_util_max " (since Linux 5.3)"
.TP
.I sched_util_min
.TQ
.IR sched_util_max " (both since Linux 5.3)"
> +These fields specify the expected minimum and maximum utilization, respectively.
> +They are ignored unless their corresponding
> +.I SCHED_FLAG_UTIL_CLAMP_MIN
> +or
> +.I SCHED_FLAG_UTIL_CLAMP_MAX
> +are set in
> +.IR sched_flags .
> +.IP
> +Utilization is a value in the range [0..1024],
We use mathematical notation for ranges, so, assuming both 0 and 1024
are included, it would be [0, 1024].
> representing the percentage of
> +CPU time used by a task when running at the maximum frequency on the highest
> +capacity CPU of the system.
> +This is a fixed point representation, where 1024 corresponds to 100%, and 0
> +corresponds to 0%.
> +For example, a 20% utilization task is a task running for 2ms every 10ms at
> +maximum frequency and is represented by a utilization value of
> +0.2 * 1024 = 205.
> +.IP
> +A task with a minimum utilization value larger than 0 is more likely scheduled
> +on a CPU with a capacity big enough to fit the specified value.
> +A task with a maximum utilization value smaller than 1024 is more likely
> +scheduled on a CPU with no more capacity than the specified value.
> +.IP
> +A task utilization boundary can be reset by setting its field to
> +.I UINT32_MAX
Macro names are written in bold, not italics.
> +(new in Linux 5.11).
> .P
> The
> .I flags
> @@ -353,7 +398,6 @@ .SH ERRORS
> .I attr.sched_flags
> contains a flag other than
> .BR SCHED_FLAG_RESET_ON_FORK ;
> -or
This change seems to be unrelated to this patch, right?
> .I attr.sched_priority
> is invalid; or
> .I attr.sched_policy
> @@ -363,6 +407,23 @@ .SH ERRORS
> .I attr
> are invalid.
> .TP
> +.B EINVAL
> +.I attr.sched_flags
> +contains
> +.B SCHED_FLAG_UTIL_CLAMP_MIN
> +or
> +.BR SCHED_FLAG_UTIL_CLAMP_MAX ,
> +and
> +.I attr.sched_util_min
> +or
> +.I attr.sched_util_max
> +are out of bounds.
> +.TP
> +.B EOPNOTSUPP
> +SCHED_FLAG_UTIL_CLAMP was provided, but the kernel was not built with
> +.BR CONFIG_UCLAMP_TASK
> +support.
> +.TP
> .B EPERM
> The caller does not have appropriate privileges.
> .TP
> --
> 2.45.1.288.g0e0cd299f1-goog
Have a lovely day!
Alex
--
<https://www.alejandro-colomar.es/>
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