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Add new kstat for monitoring time in dmu_tx_assign

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This change adds a new kstat to gain some visibility into the amount of
time spent in each call to dmu_tx_assign. A histogram is exported via
a new dmu_tx_assign_histogram-$POOLNAME file. The information contained
in this histogram is the frequency dmu_tx_assign took to complete given
an interval range. For example, given the below histogram file:

    $ cat /proc/spl/kstat/zfs/dmu_tx_assign_histogram-tank
    12 1 0x01 32 1536 19792068076691 20516481514522
    name                            type data
    1 us                            4    859
    2 us                            4    252
    4 us                            4    171
    8 us                            4    2
    16 us                           4    0
    32 us                           4    2
    64 us                           4    0
    128 us                          4    0
    256 us                          4    0
    512 us                          4    0
    1024 us                         4    0
    2048 us                         4    0
    4096 us                         4    0
    8192 us                         4    0
    16384 us                        4    0
    32768 us                        4    1
    65536 us                        4    1
    131072 us                       4    1
    262144 us                       4    4
    524288 us                       4    0
    1048576 us                      4    0
    2097152 us                      4    0
    4194304 us                      4    0
    8388608 us                      4    0
    16777216 us                     4    0
    33554432 us                     4    0
    67108864 us                     4    0
    134217728 us                    4    0
    268435456 us                    4    0
    536870912 us                    4    0
    1073741824 us                   4    0
    2147483648 us                   4    0

one can see most calls to dmu_tx_assign completed in 32us or less, but a
few outliers did not. Specifically, 4 of the calls took between 262144us
and 131072us. This information is difficult, if not impossible, to gather
without this change.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1584
This commit is contained in:
Prakash Surya
2013-07-10 15:53:48 -07:00
committed by Brian Behlendorf
parent bf89c19914
commit 92334b14ec
3 changed files with 72 additions and 0 deletions
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module/zfs/dmu_tx.c
+8
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@@ -1089,12 +1089,15 @@ dmu_tx_unassign(dmu_tx_t *tx)
int
dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how)
{
hrtime_t before, after;
int err;
ASSERT(tx->tx_txg == 0);
ASSERT(txg_how != 0);
ASSERT(!dsl_pool_sync_context(tx->tx_pool));
before = gethrtime();
while ((err = dmu_tx_try_assign(tx, txg_how)) != 0) {
dmu_tx_unassign(tx);
@@ -1106,6 +1109,11 @@ dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how)
txg_rele_to_quiesce(&tx->tx_txgh);
after = gethrtime();
dsl_pool_tx_assign_add_usecs(tx->tx_pool,
(after - before) / NSEC_PER_USEC);
return (0);
}