illumos gate

The function txg_delay() is used to delay txg (transaction group) threads in ZFS.
The timeout value for this function is calculated using:

int timeout = ddi_get_lbolt() + ticks;

Later, the actual wait is performed:

        while (ddi_get_lbolt() < timeout &&
            tx->tx_syncing_txg < txg-1 && !txg_stalled(dp))
                (void) cv_timedwait(&tx->tx_quiesce_more_cv, &tx->tx_sync_lock,
                    timeout - ddi_get_lbolt());

The ddi_get_lbolt() function returns current uptime in clock ticks and is typed as clock_t.
The clock_t type on 64-bit architectures is int64_t.

The "timeout" variable will overflow depending on the tick frequency (e.g. for 1000 it will overflow in 28.855 days). This will make the expression "ddi_get_lbolt() < timeout" always false - txg threads will not be delayed anymore at all. This leads to a slowdown in ZFS writes.

The attached patch initializes timeout as clock_t to match the return value of ddi_get_lbolt().