Date: Sun, 19 May 2019 05:46:24 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r347966 - head/share/man/man4 Message-ID: <201905190546.x4J5kOkO027339@repo.freebsd.org>
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Author: imp Date: Sun May 19 05:46:24 2019 New Revision: 347966 URL: https://svnweb.freebsd.org/changeset/base/347966 Log: Add note about nvd / nda selection. Noticed by: cem@ Modified: head/share/man/man4/nvme.4 Modified: head/share/man/man4/nvme.4 ============================================================================== --- head/share/man/man4/nvme.4 Sun May 19 04:56:02 2019 (r347965) +++ head/share/man/man4/nvme.4 Sun May 19 05:46:24 2019 (r347966) @@ -33,7 +33,7 @@ .\" .\" $FreeBSD$ .\" -.Dd December 7, 2018 +.Dd May 18, 2019 .Dt NVME 4 .Os .Sh NAME @@ -119,6 +119,38 @@ hw.nvme.force_intx=1 .Ed .Pp Note that use of INTx implies disabling of per-CPU I/O queue pairs. +.Pp +The +.Xr nvd 4 +driver is used to provide a disk driver to the system by default. +The +.Xr nda 4 +driver can also be used instead. +The +.Xr nvd 4 +driver performs better with smaller transactions and few TRIM +commands. +It sends all commands directly the drive immediately. +The +.Xr nda 4 +driver performs better with larger transactions and also collapses +TRIM commands giving better performance. +It can queue commands to the drive; combine +.Dv BIO_DELETE +commands into a single trip; and +use the CAM I/O scheduler to bias one type of operation over another. +To select the +.Xr nda 4 +driver, set the following tunable value in +.Xr loader.conf 5 : +.Bd -literal -offset indent +hw.nvme.use_nvd=0 +.Ed +.Pp +This value may also be set in the kernel config file with +.Bd -literal -offset indent +.Cd options NVME_USE_NVD=0 +.Ed .Sh SYSCTL VARIABLES The following controller-level sysctls are currently implemented: .Bl -tag -width indent
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