| Message ID | 20160614081125.GA17700@js1304-P5Q-DELUXE (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Joonsoo, On Tue, Jun 14, 2016 at 10:11 AM, Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote: > On Tue, Jun 14, 2016 at 09:31:23AM +0200, Geert Uytterhoeven wrote: >> On Tue, Jun 14, 2016 at 8:24 AM, Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote: >> > On Mon, Jun 13, 2016 at 09:43:13PM +0200, Geert Uytterhoeven wrote: >> >> On Tue, Apr 12, 2016 at 6:51 AM, <js1304@gmail.com> wrote: >> >> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com> >> >> > To check whther free objects exist or not precisely, we need to grab a >> >> > lock. But, accuracy isn't that important because race window would be >> >> > even small and if there is too much free object, cache reaper would reap >> >> > it. So, this patch makes the check for free object exisistence not to >> >> > hold a lock. This will reduce lock contention in heavily allocation case. >> >> > >> >> > Note that until now, n->shared can be freed during the processing by >> >> > writing slabinfo, but, with some trick in this patch, we can access it >> >> > freely within interrupt disabled period. >> >> > >> >> > Below is the result of concurrent allocation/free in slab allocation >> >> > benchmark made by Christoph a long time ago. I make the output simpler. >> >> > The number shows cycle count during alloc/free respectively so less is >> >> > better. >> >> > >> >> > * Before >> >> > Kmalloc N*alloc N*free(32): Average=248/966 >> >> > Kmalloc N*alloc N*free(64): Average=261/949 >> >> > Kmalloc N*alloc N*free(128): Average=314/1016 >> >> > Kmalloc N*alloc N*free(256): Average=741/1061 >> >> > Kmalloc N*alloc N*free(512): Average=1246/1152 >> >> > Kmalloc N*alloc N*free(1024): Average=2437/1259 >> >> > Kmalloc N*alloc N*free(2048): Average=4980/1800 >> >> > Kmalloc N*alloc N*free(4096): Average=9000/2078 >> >> > >> >> > * After >> >> > Kmalloc N*alloc N*free(32): Average=344/792 >> >> > Kmalloc N*alloc N*free(64): Average=347/882 >> >> > Kmalloc N*alloc N*free(128): Average=390/959 >> >> > Kmalloc N*alloc N*free(256): Average=393/1067 >> >> > Kmalloc N*alloc N*free(512): Average=683/1229 >> >> > Kmalloc N*alloc N*free(1024): Average=1295/1325 >> >> > Kmalloc N*alloc N*free(2048): Average=2513/1664 >> >> > Kmalloc N*alloc N*free(4096): Average=4742/2172 >> >> > >> >> > It shows that allocation performance decreases for the object size up to >> >> > 128 and it may be due to extra checks in cache_alloc_refill(). But, with >> >> > considering improvement of free performance, net result looks the same. >> >> > Result for other size class looks very promising, roughly, 50% performance >> >> > improvement. >> >> > >> >> > v2: replace kick_all_cpus_sync() with synchronize_sched(). >> >> > >> >> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> >> >> >> >> I've bisected a boot failure (no output at all) in v4.7-rc2 on emev2/kzm9d >> >> (Renesas dual Cortex A9) to this patch, which is upstream commit >> >> 801faf0db8947e01877920e848a4d338dd7a99e7. >> >> >> >> I've attached my .config. I don't know if it also happens with >> >> shmobile_defconfig, as something went wrong with my remote access to the board, >> >> preventing further testing. I also couldn't verify if the issue persists in >> >> v4.7-rc3. >> >> In the mean time, I've verified it also happens with shmobile_defconfig. >> >> >> Do you have a clue? >> > >> > I don't have yet. Could you help me to narrow down the problem? >> > Following diff is half-revert change to check that synchronize_sched() >> > has no problem. >> >> Thanks! >> >> Unfortunately the half revert is not sufficient. The full revert is. > > Thanks for quick testing! > > Could I ask one more time to check that synchronize_sched() is root > cause of the problem? Testing following two diffs will be helpful to me. > > Thanks. > > ------->8-------- > diff --git a/mm/slab.c b/mm/slab.c > index 763096a..d892364 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -965,7 +965,7 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, > * freed after synchronize_sched(). > */ > if (force_change) > - synchronize_sched(); > + kick_all_cpus_sync(); > > fail: > kfree(old_shared); Works. > ------->8------ > diff --git a/mm/slab.c b/mm/slab.c > index 763096a..38d99c2 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -964,8 +964,6 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, > * guaranteed to be valid until irq is re-enabled, because it will be > * freed after synchronize_sched(). > */ > - if (force_change) > - synchronize_sched(); > > fail: > kfree(old_shared); > Also works. Note that I do not see this problem on any of the other boards I use, one of which is also a dual Cortex A9. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
diff --git a/mm/slab.c b/mm/slab.c index 763096a..d892364 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -965,7 +965,7 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * freed after synchronize_sched(). */ if (force_change) - synchronize_sched(); + kick_all_cpus_sync(); fail: kfree(old_shared); ------->8------ diff --git a/mm/slab.c b/mm/slab.c index 763096a..38d99c2 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -964,8 +964,6 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * guaranteed to be valid until irq is re-enabled, because it will be * freed after synchronize_sched(). */ - if (force_change) - synchronize_sched(); fail: kfree(old_shared);