[PATCH v2] chrt: Add support for (GRUB) bandwidth reclaim

The SCHED_DEADLINE policy supports the (GRUB) Greedy Reclamation
of Unused Bandwidth algorithm. This allows tasks to reclaim
bandwidth that are left over by other deadline tasks that finish
their work early, or voluntarily yield the cpu.

Currently, chrt has no way to set the SCHED_FLAG_RECLAIM bit in
the sched_flags field of the sched_attr structure.

Add -G/--reclaim-grub option to allow users to toggle this feature
using the deadline scheduling class.

Signed-off-by: Furkan Caliskan <[email protected]>
---
 bash-completion/chrt   |  1 +
 schedutils/chrt.1.adoc |  3 +++
 schedutils/chrt.c      | 17 ++++++++++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/bash-completion/chrt b/bash-completion/chrt
index 3ca13fc05..363efdfa1 100644
--- a/bash-completion/chrt
+++ b/bash-completion/chrt
@@ -26,6 +26,7 @@ _chrt_module()
 				--max
 				--other
 				--pid
+				--reclaim-grub
 				--reset-on-fork
 				--rr
 				--sched-deadline
diff --git a/schedutils/chrt.1.adoc b/schedutils/chrt.1.adoc
index b8d8874bc..90a3d376a 100644
--- a/schedutils/chrt.1.adoc
+++ b/schedutils/chrt.1.adoc
@@ -81,6 +81,9 @@ Specifies period parameter for *SCHED_DEADLINE* policy (Linux-specific). Note th
 *-D*, *--sched-deadline* _nanoseconds_::
 Specifies deadline parameter for *SCHED_DEADLINE* policy (Linux-specific).
 
+*-G*, *--reclaim-grub*::
+Enables GRUB (Greedy Reclamation of Unused Bandwidth) algorithm. Linux-specific, supported since 4.13.
+
 *-R*, *--reset-on-fork*::
 Use *SCHED_RESET_ON_FORK* or *SCHED_FLAG_RESET_ON_FORK* flag. Linux-specific, supported since 2.6.31.
 +
diff --git a/schedutils/chrt.c b/schedutils/chrt.c
index 5ba9964c1..ab7e8e895 100644
--- a/schedutils/chrt.c
+++ b/schedutils/chrt.c
@@ -46,6 +46,7 @@ struct chrt_ctl {
 	uint64_t runtime;			/* --sched-* options */
 	uint64_t deadline;
 	uint64_t period;
+	uint64_t sched_flags;			/* For sched_attr->sched_flags member */
 
 	unsigned int all_tasks : 1,		/* all threads of the PID */
 		     reset_on_fork : 1,		/* SCHED_RESET_ON_FORK or SCHED_FLAG_RESET_ON_FORK */
@@ -79,6 +80,7 @@ static void __attribute__((__noreturn__)) usage(void)
 	fputs(USAGE_SEPARATOR, out);
 	fputs(_("Scheduling options:\n"), out);
 	fputs(_(" -R, --reset-on-fork       set reset-on-fork flag\n"), out);
+	fputs(_(" -G, --reclaim-grub        set SCHED_FLAG_RECLAIM\n"), out);
 	fputs(_(" -T, --sched-runtime <ns>  runtime parameter for DEADLINE\n"), out);
 	fputs(_(" -P, --sched-period <ns>   period parameter for DEADLINE\n"), out);
 	fputs(_(" -D, --sched-deadline <ns> deadline parameter for DEADLINE\n"), out);
@@ -359,6 +361,7 @@ static int set_sched_one(struct chrt_ctl *ctl, pid_t pid)
 	sa.sched_runtime  = ctl->runtime;
 	sa.sched_period   = ctl->period;
 	sa.sched_deadline = ctl->deadline;
+	sa.sched_flags    = ctl->sched_flags;
 
 # ifdef SCHED_FLAG_RESET_ON_FORK
 	/* Don't use SCHED_RESET_ON_FORK for sched_setattr()! */
@@ -417,6 +420,7 @@ int main(int argc, char **argv)
 		{ "sched-period",   required_argument, NULL, 'P' },
 		{ "sched-deadline", required_argument, NULL, 'D' },
 		{ "reset-on-fork",  no_argument,       NULL, 'R' },
+		{ "reclaim-grub",   no_argument,       NULL, 'G' },
 		{ "verbose",	no_argument, NULL, 'v' },
 		{ "version",	no_argument, NULL, 'V' },
 		{ NULL,		no_argument, NULL, 0 }
@@ -427,7 +431,7 @@ int main(int argc, char **argv)
 	textdomain(PACKAGE);
 	close_stdout_atexit();
 
-	while((c = getopt_long(argc, argv, "+abdD:efiphmoP:T:rRvV", longopts, NULL)) != -1)
+	while((c = getopt_long(argc, argv, "+abdD:efiphmoP:T:rRGvV", longopts, NULL)) != -1)
 	{
 		switch (c) {
 		case 'a':
@@ -460,6 +464,11 @@ int main(int argc, char **argv)
 		case 'R':
 			ctl->reset_on_fork = 1;
 			break;
+		case 'G':
+#ifdef SCHED_FLAG_RECLAIM
+			ctl->sched_flags |= SCHED_FLAG_RECLAIM;
+#endif
+			break;
 		case 'i':
 #ifdef SCHED_IDLE
 			ctl->policy = SCHED_IDLE;
@@ -547,6 +556,12 @@ int main(int argc, char **argv)
 	if ((ctl->deadline || ctl->period) && ctl->policy != SCHED_DEADLINE)
 		errx(EXIT_FAILURE, _("--sched-{deadline,period} options are "
 				     "supported for SCHED_DEADLINE only"));
+#ifndef HAVE_SCHED_SETATTR
+	if (ctl->sched_flags & SCHED_FLAG_RECLAIM)
+		errx(EXIT_FAILURE, _("SCHED_FLAG_RECLAIM is unsupported"));
+#endif
+	if ((ctl->sched_flags & SCHED_FLAG_RECLAIM) && ctl->policy != SCHED_DEADLINE)
+		errx(EXIT_FAILURE, _("--reclaim-grub is only supported for SCHED_DEADLINE"));
 	if (ctl->policy == SCHED_DEADLINE) {
 		/* The basic rule is runtime <= deadline <= period, so we can
 		 * make deadline and runtime optional on command line. Note we
-- 
2.34.1