| Message ID | 1367271946-7239-8-git-send-email-ccross@android.com (mailing list archive) |
|---|---|
| State | RFC, archived |
| Headers | show |
Colin, I don't know anything about when or when not to use freezable*, and I suspect that may be true for others as well. A more complete description of why it's acceptable here in the commit log might help expedite acceptance. Matt, I have a vague memory of discussing something similar to this with you. Do you see any potential problems here? -- Darren On 04/29/2013 02:45 PM, Colin Cross wrote: > Avoid waking up every thread sleeping in a futex_wait call during > suspend and resume by calling a freezable blocking call. > > Signed-off-by: Colin Cross <ccross@android.com> > --- > kernel/futex.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/futex.c b/kernel/futex.c > index b26dcfc..d710fae 100644 > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -61,6 +61,7 @@ > #include <linux/nsproxy.h> > #include <linux/ptrace.h> > #include <linux/sched/rt.h> > +#include <linux/freezer.h> > > #include <asm/futex.h> > > @@ -1807,7 +1808,7 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, > * is no timeout, or if it has yet to expire. > */ > if (!timeout || timeout->task) > - schedule(); > + freezable_schedule(); > } > __set_current_state(TASK_RUNNING); > } >
On Mon, Apr 29, 2013 at 3:52 PM, Darren Hart <dvhart@linux.intel.com> wrote: > Colin, > > I don't know anything about when or when not to use freezable*, and I > suspect that may be true for others as well. A more complete > description of why it's acceptable here in the commit log might help > expedite acceptance. > Sure, how about: This call can be converted to a freezable call because it doesn't hold any locks or release any resources when interrupted that might be needed by another freezing task or a kernel driver during suspend. -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Apr 29, 2013 at 03:52:27PM -0700, Darren Hart wrote: > Colin, > > I don't know anything about when or when not to use freezable*, and I > suspect that may be true for others as well. A more complete > description of why it's acceptable here in the commit log might help > expedite acceptance. > > > Matt, > > I have a vague memory of discussing something similar to this with you. > Do you see any potential problems here? Re: vague memories: We discussed futexes in the context of the old checkpoint/restart patch series (<= 2.6.32). This change looks correct to me. > -- > Darren > > On 04/29/2013 02:45 PM, Colin Cross wrote: > > Avoid waking up every thread sleeping in a futex_wait call during > > suspend and resume by calling a freezable blocking call. (in addition to suspend/resume: freeze/thaw via the cgroup freezer. I'm going to call it freeze/thaw since that should cover both cases..) Here's my shot at explaining what I *think* the commit is supposed fix: I imagine that before this patch on a highly-contended futex there could be a thundering herd during freeze/thaw -- the wakeups are *likely* to be painful because lots of tasks could be woken from the schedule() call by the freezer only to find that the futex state hasn't changed. With this change the freezer won't wake these tasks up because the FREEZER_SKIP flag is set while in the schedule() call and thus the thundering herd won't be triggered by the freezer. Cheers, -Matt Helsley -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/kernel/futex.c b/kernel/futex.c index b26dcfc..d710fae 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -61,6 +61,7 @@ #include <linux/nsproxy.h> #include <linux/ptrace.h> #include <linux/sched/rt.h> +#include <linux/freezer.h> #include <asm/futex.h> @@ -1807,7 +1808,7 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, * is no timeout, or if it has yet to expire. */ if (!timeout || timeout->task) - schedule(); + freezable_schedule(); } __set_current_state(TASK_RUNNING); }
Avoid waking up every thread sleeping in a futex_wait call during suspend and resume by calling a freezable blocking call. Signed-off-by: Colin Cross <ccross@android.com> --- kernel/futex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)