> From: Seth Jennings [mailto:sjenning@xxxxxxxxxxxxxxxxxx] > Sent: Friday, December 30, 2011 9:42 AM > To: Greg Kroah-Hartman > Cc: Seth Jennings; Dan Magenheimer; Brian King; devel@xxxxxxxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: [PATCH] staging: zcache: fix serialization bug in zv stats > > In a multithreaded workload, the zv_curr_dist_counts > and zv_cumul_dist_counts statistics are being corrupted > because the increments and decrements in zv_create > and zv_free are not atomic. > > This patch converts these statistics and their corresponding > increments/decrements/reads to atomic operations. > > Based on v3.2-rc7 > > Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx> I'm inclined to nack this change, at least unless inside an #ifdef DEBUG, as these counts are interesting to a developer but not useful to a normal end user, whereas the incremental cost for atomic_inc and atomic_dec are non-trivial. I don't think any off-by-one in these counters could result in a bug and, before promotion from staging, they probably should just go away. (They are fun to "watch -d" though ;-) That said, as a developer, I too am annoyed by the occasional 64-bit "negative unsigned" that show up in the output but IMHO a good fix for that might be simply for the "show" routine to convert negative values to zero before printing. > --- > drivers/staging/zcache/zcache-main.c | 14 +++++++------- > 1 files changed, 7 insertions(+), 7 deletions(-) > > diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c > index 56c1f9c..d39bb51 100644 > --- a/drivers/staging/zcache/zcache-main.c > +++ b/drivers/staging/zcache/zcache-main.c > @@ -655,8 +655,8 @@ static unsigned int zv_max_zsize = (PAGE_SIZE / 8) * 7; > */ > static unsigned int zv_max_mean_zsize = (PAGE_SIZE / 8) * 5; > > -static unsigned long zv_curr_dist_counts[NCHUNKS]; > -static unsigned long zv_cumul_dist_counts[NCHUNKS]; > +static atomic_t zv_curr_dist_counts[NCHUNKS]; > +static atomic_t zv_cumul_dist_counts[NCHUNKS]; > > static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id, > struct tmem_oid *oid, uint32_t index, > @@ -675,8 +675,8 @@ static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id, > &page, &offset, ZCACHE_GFP_MASK); > if (unlikely(ret)) > goto out; > - zv_curr_dist_counts[chunks]++; > - zv_cumul_dist_counts[chunks]++; > + atomic_inc(&zv_curr_dist_counts[chunks]); > + atomic_inc(&zv_cumul_dist_counts[chunks]); > zv = kmap_atomic(page, KM_USER0) + offset; > zv->index = index; > zv->oid = *oid; > @@ -698,7 +698,7 @@ static void zv_free(struct xv_pool *xvpool, struct zv_hdr *zv) > > ASSERT_SENTINEL(zv, ZVH); > BUG_ON(chunks >= NCHUNKS); > - zv_curr_dist_counts[chunks]--; > + atomic_dec(&zv_curr_dist_counts[chunks]); > size -= sizeof(*zv); > BUG_ON(size == 0); > INVERT_SENTINEL(zv, ZVH); > @@ -738,7 +738,7 @@ static int zv_curr_dist_counts_show(char *buf) > char *p = buf; > > for (i = 0; i < NCHUNKS; i++) { > - n = zv_curr_dist_counts[i]; > + n = atomic_read(&zv_curr_dist_counts[i]); > p += sprintf(p, "%lu ", n); > chunks += n; > sum_total_chunks += i * n; > @@ -754,7 +754,7 @@ static int zv_cumul_dist_counts_show(char *buf) > char *p = buf; > > for (i = 0; i < NCHUNKS; i++) { > - n = zv_cumul_dist_counts[i]; > + n = atomic_read(&zv_cumul_dist_counts[i]); > p += sprintf(p, "%lu ", n); > chunks += n; > sum_total_chunks += i * n; > -- > 1.7.5.4 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
