svn commit: r355831 - head/sys/cam/nvme

[Steven Hartland]

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 */
>