lkml.org 
[lkml]   [2018]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v5 02/15] sched/core: make sched_setattr able to tune the current policy
Date
Currently, sched_setattr mandates that a policy is always specified.
Since utilization clamp attributes could apply across different
scheduling policies (i.e. all but SCHED_DEADLINE), this requires also
to always know which policy a task has before changing its clamp values.

This is not just cumbersome but it's also racy, indeed we cannot be
sure that a task policy has been changed in between its policy read and
the actual clamp value change. Sometimes however, this could be the
actual use-case, we wanna change the clamps without affecting the
policy.

Let's fix this adding an additional attribute flag
(SCHED_FLAG_TUNE_POLICY) which, when specified, will ensure to always
force the usage of the current policy. This is done by re-using the
SETPARAM_POLICY thing we already have for the sched_setparam syscall,
thus extending its usage to the non-POSIX sched_setattr while not
exposing that internal concept to user-space.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: linux-api@vger.kernel.org

---
Changes in v5:
Message-ID: <20180905110108.GC20267@localhost.localdomain>
- allow to change clamp values without affecting current policy
---
include/uapi/linux/sched.h | 6 +++++-
kernel/sched/core.c | 11 ++++++++++-
2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index c27d6e81517b..62498d749bec 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -40,6 +40,8 @@
/* SCHED_ISO: reserved but not implemented yet */
#define SCHED_IDLE 5
#define SCHED_DEADLINE 6
+/* Must be the last entry: used check attr.policy values */
+#define SCHED_POLICY_MAX 7

/* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */
#define SCHED_RESET_ON_FORK 0x40000000
@@ -50,11 +52,13 @@
#define SCHED_FLAG_RESET_ON_FORK 0x01
#define SCHED_FLAG_RECLAIM 0x02
#define SCHED_FLAG_DL_OVERRUN 0x04
-#define SCHED_FLAG_UTIL_CLAMP 0x08
+#define SCHED_FLAG_TUNE_POLICY 0x08
+#define SCHED_FLAG_UTIL_CLAMP 0x10

#define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \
SCHED_FLAG_RECLAIM | \
SCHED_FLAG_DL_OVERRUN | \
+ SCHED_FLAG_TUNE_POLICY | \
SCHED_FLAG_UTIL_CLAMP)

#endif /* _UAPI_LINUX_SCHED_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3701bb1e6698..9a2e12eaa377 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4595,8 +4595,17 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
if (retval)
return retval;

- if ((int)attr.sched_policy < 0)
+ /*
+ * A valid policy has always to be required from userspace. Unless
+ * the SCHED_FLAG_TUNE_POLICY is set, in which case, the current
+ * policy will be enforced for this call.
+ */
+ if (attr.sched_policy >= SCHED_POLICY_MAX &&
+ !(attr.sched_flags & SCHED_FLAG_TUNE_POLICY)) {
return -EINVAL;
+ }
+ if (attr.sched_flags & SCHED_FLAG_TUNE_POLICY)
+ attr.sched_policy = SETPARAM_POLICY;

rcu_read_lock();
retval = -ESRCH;
--
2.18.0
\
 
 \ /
  Last update: 2018-10-29 19:37    [W:0.312 / U:7.292 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site