Be aware that ZFS already does a pretty decent job of this already, so
the statement
about upper layers isn't true for all. It even has different priorities
for different request
types so I'm a little concerned that doing it at both layers could cause
issues.
In addition to this if its anything like SSD's numbers of requests are
only a small part
of the story with total trim size being the other one. I this case you
could hit total
desired size with just one BIO_DELETE request.
With this code what's the impact of this?
On 17/12/2019 00:11, Warner Losh wrote:
Author: imp
Date: Tue Dec 17 00:11:48 2019
New Revision: 355831
URL: https://svnweb.freebsd.org/changeset/base/355831
Log:
NVME trim stuff.
Add two sysctls to control pacing of nvme
trims. kern.cam.nda.X.goal_trim is the number of upper layer
BIO_DEELETE requests to try to collecet before sending TRIM down too
the nvme drive. trim_ticks is the number of ticks, at mosot, to wait
for at least goal_trim BIOS_DELEETE requests to come in.
Trim pacing is useful when a large number off disjoint trims are
comoing in from the upper layers. Since we have no way to chain
toogether trims from the upper layers that are sent down, this acts as
a hueristic to group trims into reasonable sized chunks. What's
reasonable varies from drive to drive.
Sponsored by: Netflix
Modified:
head/sys/cam/nvme/nvme_da.c
Modified: head/sys/cam/nvme/nvme_da.c
==============================================================================
--- head/sys/cam/nvme/nvme_da.c Tue Dec 17 00:10:19 2019 (r355830)
+++ head/sys/cam/nvme/nvme_da.c Tue Dec 17 00:11:48 2019 (r355831)
@@ -177,6 +177,14 @@ static int nda_max_trim_entries = NDA_MAX_TRIM_ENTRIES
SYSCTL_INT(_kern_cam_nda, OID_AUTO, max_trim, CTLFLAG_RDTUN,
&nda_max_trim_entries, NDA_MAX_TRIM_ENTRIES,
"Maximum number of BIO_DELETE to send down as a DSM TRIM.");
+static int nda_goal_trim_entries = NDA_MAX_TRIM_ENTRIES / 2;
+SYSCTL_INT(_kern_cam_nda, OID_AUTO, goal_trim, CTLFLAG_RDTUN,
+ &nda_goal_trim_entries, NDA_MAX_TRIM_ENTRIES / 2,
+ "Number of BIO_DELETE to try to accumulate before sending a DSM TRIM.");
+static int nda_trim_ticks = 50; /* 50ms ~ 1000 Hz */
+SYSCTL_INT(_kern_cam_nda, OID_AUTO, trim_ticks, CTLFLAG_RDTUN,
+ &nda_trim_ticks, 50,
+ "Number of ticks to hold BIO_DELETEs before sending down a trim");
/*
* All NVMe media is non-rotational, so all nvme device instances
@@ -741,6 +749,9 @@ ndaregister(struct cam_periph *periph, void *arg)
free(softc, M_DEVBUF);
return(CAM_REQ_CMP_ERR);
}
+ /* Statically set these for the moment */
+ cam_iosched_set_trim_goal(softc->cam_iosched, nda_goal_trim_entries);
+ cam_iosched_set_trim_ticks(softc->cam_iosched, nda_trim_ticks);
/* ident_data parsing */
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