Bug 200316

Summary:

[dtrace] don't have compiler inline vdev_queue_max_async_writes so zfs write throttle tuning works

Product:

Base System

Reporter:

Lacey Powers <lacey.leanne>

Component:

kern

Assignee:

Allan Jude <allanjude>

Status:

Closed FIXED

Severity:

Affects Only Me

CC:

allanjude, gnn, jch

Priority:

---

Keywords:

patch

Version:

10.1-RELEASE

Hardware:

Any

OS:

Any

Attachments:

Description	Flags
patch against 10.1-RELEASE to fix the issue.	none
q.d script to reproduce the issue	none

Description Lacey Powers 2015-05-19 03:34:55 UTC

Created attachment 156921 [details]
patch against 10.1-RELEASE to fix the issue.

On unpatched systems vdev_queue_max_async_writes is inlined and hidden from dtrace. 

This prevents the use of the q.d async write tuning script, as outlined here

http://dtrace.org/blogs/ahl/2014/08/31/openzfs-tuning/

which makes it difficult to properly investigate and tune the ZFS write throttle on FreeBSD 10.1. 

On unpatched systems the script reports:

dtrace: failed to compile script ./q.d: line 6: probe description fbt::vdev_queue_max_async_writes:entry does not match any probes

Once patched, the output looks like this:

     min .--------------------------------. max      | count
     < 0 :  █                             : >= 30    | 174


     min .--------------------------------. max      | count
     < 0 :                                : >= 30    | 0


The attached patch adding __noinline fixes this. 

The problem can be reproduced on unpatched systems with the attached q.d script.

Thank you for your time and assistance in fixing this.

Comment 1 Lacey Powers 2015-05-19 03:35:35 UTC

Created attachment 156922 [details]
q.d script to reproduce the issue

Comment 2 commit-hook freebsd_committer

2015-08-31 23:10:58 UTC

A commit references this bug:

Author: allanjude
Date: Mon Aug 31 23:10:43 UTC 2015
New revision: 287337
URL: https://svnweb.freebsd.org/changeset/base/287337

Log:
  Apply the noline attribute to vdev_queue_max_async_writes

  This makes it possible to analyze the performance of the new ZFS
  write throttle with dtrace

  PR:		200316
  Submitted by:	Lacey Powers <lacey.leanne@gmail.com>
  Reviewed by:	avg, smh, delphij (no objection)
  Approved by:	bapt (mentor)
  MFC after:	1 month
  Sponsored by:	ScaleEngine Inc.
  Differential Revision:	https://reviews.freebsd.org/D3472

Changes:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c

Comment 3 commit-hook freebsd_committer

2016-01-16 18:40:31 UTC

A commit references this bug:

Author: allanjude
Date: Sat Jan 16 18:39:55 UTC 2016
New revision: 294188
URL: https://svnweb.freebsd.org/changeset/base/294188

Log:
  MFC: r287337
    Apply the noline attribute to vdev_queue_max_async_writes

    This makes it possible to analyze the performance of the new ZFS
    write throttle with dtrace

  PR:		200316
  Sponsored by:	FreeBSD Mastery: Advanced ZFS

Changes:
_U  stable/10/
  stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c