hi Yiteng,
On Mon, Jul 22, 2019 at 03:23:08PM -0400, Jonathan Rajotte-Julien wrote:
> Hi Yiteng,
>
> On Mon, Jul 22, 2019 at 02:44:09PM -0400, Yiteng Guo wrote:
> > Hi Jonathan,
> >
> > I spent these days on this problem and finally figured it out. Here
> > are patches I've written.
>
> Sorry for that, I had other stuff ongoing.
>
> I had a brief discussion about this with Mathieu Desnoyers.
>
> Mathieu mentioned that the page faults you are seeing might be related to
> qemu/kvm usage of KSM [1]. I did not have time to play around with it and see
> if
> this indeed have an effect. You might be better off trying it since you are
> already all setup. Might want to disable it and retry your experiment (if only
> doing this on a vm).
Disregard all of this for now. I think we misunderstood the first email and got
too far too fast.
I modified lttng-ust to use MAP_POPULATE and based on the result from the
page_fault
perf counter it seems to achieve what you are looking for.
See attached patch. Let me know if this help.
Cheers.
--
Jonathan Rajotte-Julien
EfficiOS
>From 2b065e5988067291e3367f413571248f4551acb2 Mon Sep 17 00:00:00 2001
From: Jonathan Rajotte <jonathan.rajotte-jul...@efficios.com>
Date: Mon, 22 Jul 2019 17:37:43 -0400
Subject: [PATCH lttng-ust] Use MAP_POPULATE to reduce pagefault
Signed-off-by: Jonathan Rajotte <jonathan.rajotte-jul...@efficios.com>
---
libringbuffer/shm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libringbuffer/shm.c b/libringbuffer/shm.c
index 10b3bcef..489322e6 100644
--- a/libringbuffer/shm.c
+++ b/libringbuffer/shm.c
@@ -154,7 +154,7 @@ struct shm_object *_shm_object_table_alloc_shm(struct shm_object_table *table,
/* memory_map: mmap */
memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
- MAP_SHARED, shmfd, 0);
+ MAP_SHARED | MAP_POPULATE, shmfd, 0);
if (memory_map == MAP_FAILED) {
PERROR("mmap");
goto error_mmap;
@@ -341,7 +341,7 @@ struct shm_object *shm_object_table_append_shm(struct shm_object_table *table,
/* memory_map: mmap */
memory_map = mmap(NULL, memory_map_size, PROT_READ | PROT_WRITE,
- MAP_SHARED, shm_fd, 0);
+ MAP_SHARED | MAP_POPULATE, shm_fd, 0);
if (memory_map == MAP_FAILED) {
PERROR("mmap");
goto error_mmap;
--
2.17.1
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