The sloppy nature of lockless access to percpu pointers
(s->current_path) in rr_select_path(), from multiple threads, is
causing some paths to used more than others -- which results in less
IO performance being observed.
Revert these upstream commits to restore truly symmetric round-robin
IO submission in DM multipath:
b0b477c dm round robin: use percpu 'repeat_count' and 'current_path'
802934b dm round robin: do not use this_cpu_ptr() without having preemption disabled
There is no benefit to all this complexity if repeat_count = 1 (which is
the recommended default).
Cc: stable@vger.kernel.org # 4.6+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Use local_irq_save() to disable preemption before calling
this_cpu_ptr().
Reported-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Fixes: b0b477c7e0 ("dm round robin: use percpu 'repeat_count' and 'current_path'")
Cc: stable@vger.kernel.org # 4.6+
Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Now that dm-mpath core is lockless in the per-IO fast path it is
critical, for performance, to have the .select_path hook
(rr_select_path) also be as lockless as possible.
The new percpu members of 'struct selector' allow for lockless support
of 'repeat_count' governed repeat use of a previously selected path. If
a path fails while it is 'current_path' the worst case is concurrent IO
might be mapped to the failed path until the .fail_path hook
(rr_fail_path) is called.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
If a path selector has any use for a repeat_count it should be handled
locally and not depend on the dm-mpath core to be concerned with it.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Proper locking of the lists used by the path selectors should be handled
within the selectors (relying on dm-mpath.c code's use of the m->lock
spinlock was reckless).
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Preparation for making __multipath_map() avoid taking the m->lock
spinlock -- in favor of using RCU locking.
repeat_count was primarily for bio-based DM multipath's benefit. There
is really no need for it anymore now that DM multipath is request-based.
As such, repeat_count > 1 is no longer honored and a warning is
displayed if the user attempts to use a value > 1. This is a temporary
change for the round-robin path-selector (as a later commit will restore
its support for repeat_count > 1).
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Device mapper uses sscanf to convert arguments to numbers. The problem is that
the way we use it ignores additional unmatched characters in the scanned string.
For example, this `if (sscanf(string, "%d", &number) == 1)' will match a number,
but also it will match number with some garbage appended, like "123abc".
As a result, device mapper accepts garbage after some numbers. For example
the command `dmsetup create vg1-new --table "0 16384 linear 254:1bla 34816bla"'
will pass without an error.
This patch fixes all sscanf uses in device mapper. It appends "%c" with
a pointer to a dummy character variable to every sscanf statement.
The construct `if (sscanf(string, "%d%c", &number, &dummy) == 1)' succeeds
only if string is a null-terminated number (optionally preceded by some
whitespace characters). If there is some character appended after the number,
sscanf matches "%c", writes the character to the dummy variable and returns 2.
We check the return value for 1 and consequently reject numbers with some
garbage appended.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
A pending cleanup will mean that module.h won't be implicitly
everywhere anymore. Make sure the modular drivers in md dir
are actually calling out for <module.h> explicitly in advance.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
This patch makes two additions to the dm path selector interface for
dynamic load balancers:
o a new hook, start_io()
o a new parameter 'nr_bytes' to select_path()/start_io()/end_io()
to pass the size of the I/O
start_io() is called when a target driver actually submits I/O
to the selected path.
Path selectors can use it to start accounting of the I/O.
(e.g. counting the number of in-flight I/Os.)
The start_io hook is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html
nr_bytes, the size of the I/O, is so path selectors can take the
size of the I/O into account when deciding which path to use.
dm-service-time uses it to estimate service time, for example.
(Added the nr_bytes member to dm_mpath_io instead of using existing
details.bi_size, since request-based dm patch deletes it.)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Change #include "dm.h" to #include <linux/device-mapper.h> in all targets.
Targets should not need direct access to internal DM structures.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Remove explicit module name from messages as the macro now includes it
automatically.
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rename DM's struct path to struct dm_path to prevent name collision between it
and struct path from fs/namei.c.
Signed-off-by: Josef "Jeff" Sipek <jsipek@cs.sunysb.edu>
Acked-by: Alasdair G Kergon <agk@redhat.com>
Cc: <reiserfs-dev@namesys.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
When adding paths to the round-robin path selector, their order gets inverted,
which is not desirable.
Fix by replacing list_add() with list_add_tail().
Signed-off-by: Jonathan E Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: <dm-devel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Tidy device-mapper error messages to include context information
automatically.
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Mike Snitzer