On Mon, 2015-07-27 at 09:08 +0200, Michal Hocko wrote:
> On Fri 24-07-15 09:56:27, Jörn Engel wrote:
> > On Fri, Jul 24, 2015 at 09:04:21AM +0200, Michal Hocko wrote:
> > > On Thu 23-07-15 14:54:33, Spencer Baugh wrote:
> > > > From: Joern Engel <joern@xxxxxxxxx>
> > > >
> > > > Mapping large memory spaces can be slow and prevent high-priority
> > > > realtime threads from preempting lower-priority threads for a long time.
> > >
> > > How can a lower priority task block the high priority one? Do you have
> > > preemption disabled?
> >
> > Yes.
>
> Yes what? PREEMT enabled and still low priority task starving a high
> priority one? What is your exact setup?
There are other places that are pretty horrible too if you don't run a
PREEMPT kernel. Spending milliseconds in kernel kinda takes the real
outta realtime, even for the most casual of users.
(ponder: preempt kernel for rt only, rt could have decent latency
without driving normal task throughput through the floor)
kbuild make -j8 + cyclictest -Smp99
PREEMPT_VOLUNTARY Before:
T: 0 ( 6459) P:99 I:1000 C: 286022 Min: 1 Act: 1 Avg: 5 Max: 1718
T: 1 ( 6460) P:99 I:1500 C: 190701 Min: 1 Act: 1 Avg: 5 Max: 1639
T: 2 ( 6461) P:99 I:2000 C: 143024 Min: 1 Act: 2 Avg: 5 Max: 2504
T: 3 ( 6462) P:99 I:2500 C: 114420 Min: 1 Act: 1 Avg: 5 Max: 1922
T: 4 ( 6463) P:99 I:3000 C: 95350 Min: 1 Act: 1 Avg: 5 Max: 1482
T: 5 ( 6464) P:99 I:3500 C: 81728 Min: 1 Act: 2 Avg: 5 Max: 1496
T: 6 ( 6465) P:99 I:4000 C: 71511 Min: 1 Act: 1 Avg: 5 Max: 1813
T: 7 ( 6466) P:99 I:4500 C: 63566 Min: 1 Act: 1 Avg: 5 Max: 1901
PREEMPT_VOLUNTARY After:
T: 0 ( 6997) P:99 I:1000 C: 286032 Min: 1 Act: 2 Avg: 3 Max: 125
T: 1 ( 6998) P:99 I:1500 C: 190687 Min: 1 Act: 1 Avg: 4 Max: 130
T: 2 ( 6999) P:99 I:2000 C: 143015 Min: 1 Act: 1 Avg: 4 Max: 97
T: 3 ( 7000) P:99 I:2500 C: 114411 Min: 1 Act: 2 Avg: 4 Max: 90
T: 4 ( 7001) P:99 I:3000 C: 95341 Min: 1 Act: 1 Avg: 4 Max: 139
T: 5 ( 7002) P:99 I:3500 C: 81722 Min: 1 Act: 2 Avg: 4 Max: 112
T: 6 ( 7003) P:99 I:4000 C: 71506 Min: 1 Act: 2 Avg: 4 Max: 137
T: 7 ( 7004) P:99 I:4500 C: 63561 Min: 1 Act: 2 Avg: 4 Max: 109
---
mm/memory.c | 8 ++++++--
mm/page_alloc.c | 1 +
2 files changed, 7 insertions(+), 2 deletions(-)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1174,8 +1174,10 @@ static unsigned long zap_pte_range(struc
force_flush = 0;
tlb_flush_mmu_free(tlb);
- if (addr != end)
+ if (addr != end) {
+ cond_resched();
goto again;
+ }
}
return addr;
@@ -1336,8 +1338,10 @@ void unmap_vmas(struct mmu_gather *tlb,
struct mm_struct *mm = vma->vm_mm;
mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
- for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
+ for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
+ cond_resched();
+ }
mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
}
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1934,6 +1934,7 @@ void free_hot_cold_page_list(struct list
list_for_each_entry_safe(page, next, list, lru) {
trace_mm_page_free_batched(page, cold);
free_hot_cold_page(page, cold);
+ cond_resched();
}
}
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