What if any is the impact on request ordering with this new delayed TRIM?
On 17/12/2019 00:13, Warner Losh wrote:
Author: imp
Date: Tue Dec 17 00:13:21 2019
New Revision: 355832
URL: https://svnweb.freebsd.org/changeset/base/355832
Log:
Add rate limiters to TRIM.
Add rate limiters to trims. Trims are a bit different than reads or
writes in that they can be combined, so some care needs to be taken
where we rate limit them. Additional work will be needed to push the
working rate limit below the I/O quanta rate for things like IOPS.
Sponsored by: Netflix
Modified:
head/sys/cam/cam_iosched.c
Modified: head/sys/cam/cam_iosched.c
==============================================================================
--- head/sys/cam/cam_iosched.c Tue Dec 17 00:11:48 2019 (r355831)
+++ head/sys/cam/cam_iosched.c Tue Dec 17 00:13:21 2019 (r355832)
@@ -755,7 +755,20 @@ cam_iosched_has_io(struct cam_iosched_softc *isc)
static inline bool
cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
{
+ struct bio *bp;
+ bp = bioq_first(&isc->trim_queue);
+#ifdef CAM_IOSCHED_DYNAMIC
+ if (do_dynamic_iosched) {
+ /*
+ * If we're limiting trims, then defer action on trims
+ * for a bit.
+ */
+ if (bp == NULL || cam_iosched_limiter_caniop(&isc->trim_stats,
bp) != 0)
+ return false;
+ }
+#endif
+
/*
* If we've set a trim_goal, then if we exceed that allow trims
* to be passed back to the driver. If we've also set a tick timeout
@@ -771,8 +784,8 @@ cam_iosched_has_more_trim(struct cam_iosched_softc *is
return false;
}
- return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) &&
- bioq_first(&isc->trim_queue);
+ /* NB: Should perhaps have a max trim active independent of I/O
limiters */
+ return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) && bp != NULL;
}
#define cam_iosched_sort_queue(isc) ((isc)->sort_io_queue >= 0 ? \
@@ -1389,10 +1402,17 @@ cam_iosched_next_trim(struct cam_iosched_softc *isc)
struct bio *
cam_iosched_get_trim(struct cam_iosched_softc *isc)
{
+#ifdef CAM_IOSCHED_DYNAMIC
+ struct bio *bp;
+#endif
if (!cam_iosched_has_more_trim(isc))
return NULL;
#ifdef CAM_IOSCHED_DYNAMIC
+ bp = bioq_first(&isc->trim_queue);
+ if (bp == NULL)
+ return NULL;
+
/*
* If pending read, prefer that based on current read bias setting. The
* read bias is shared for both writes and TRIMs, but on TRIMs the bias
@@ -1414,6 +1434,26 @@ cam_iosched_get_trim(struct cam_iosched_softc *isc)
*/
isc->current_read_bias = isc->read_bias;
}
+
+ /*
+ * See if our current limiter allows this I/O. Because we only call this
+ * here, and not in next_trim, the 'bandwidth' limits for trims won't
+ * work, while the iops or max queued limits will work. It's tricky
+ * because we want the limits to be from the perspective of the
+ * "commands sent to the device." To make iops work, we need to check
+ * only here (since we want all the ops we combine to count as one). To
+ * make bw limits work, we'd need to check in next_trim, but that would
+ * have the effect of limiting the iops as seen from the upper layers.
+ */
+ if (cam_iosched_limiter_iop(&isc->trim_stats, bp) != 0) {
+ if (iosched_debug)
+ printf("Can't trim because limiter says no.\n");
+ isc->trim_stats.state_flags |= IOP_RATE_LIMITED;
+ return NULL;
+ }
+ isc->current_read_bias = isc->read_bias;
+ isc->trim_stats.state_flags &= ~IOP_RATE_LIMITED;
+ /* cam_iosched_next_trim below keeps proper book */
#endif
return cam_iosched_next_trim(isc);
}
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