kernel/drivers/md/dm-path-selector.h, branch linux-6.9.y

dm: avoid spaces before function arguments or in favour of tabs

2023-02-14T19:23:06Z

Signed-off-by: Heinz Mauelshagen Signed-off-by: Mike Snitzer

dm: change "unsigned" to "unsigned int"

2023-02-14T19:23:06Z

Signed-off-by: Heinz Mauelshagen Signed-off-by: Mike Snitzer

dm: add missing SPDX-License-Indentifiers

2023-02-14T19:23:06Z

'GPL-2.0-only' is used instead of 'GPL-2.0' because SPDX has deprecated its use. Suggested-by: John Wiele Signed-off-by: Heinz Mauelshagen Signed-off-by: Mike Snitzer

dm mpath: provide high-resolution timer to HST for bio-based

2022-05-09T19:39:23Z

The precision loss of reading IO start_time with jiffies_to_nsecs instead of using a high resolution timer degrades HST path prediction for BIO-based mpath on high load workloads. Below, I show the utilization percentage of a 10 disk multipath with asymmetrical disk access cost, while being exercised by a randwrite FIO benchmark with high submission queue depth (depth=64). It is possible to see that the HST path selection degrades heavily for high-iops in BIO-mpath, underutilizing the slower paths way beyond expected. This seems to be caused by the start_time truncation, which makes some IO to seem much slower than it actually is. In this scenario ST outperforms HST for bio-mpath, but not for mq-mpath, which already uses ktime_get_ns(). The third column shows utilization with this patch applied. It is easy to see that now HST prediction is much closer to the ideal distribution (calculated considering the real cost of each path). | | ST | HST (orig) | HST(ktime) | Best | | sdd | 0.17 | 0.20 | 0.17 | 0.18 | | sde | 0.17 | 0.20 | 0.17 | 0.18 | | sdf | 0.17 | 0.20 | 0.17 | 0.18 | | sdg | 0.06 | 0.00 | 0.06 | 0.04 | | sdh | 0.03 | 0.00 | 0.03 | 0.02 | | sdi | 0.03 | 0.00 | 0.03 | 0.02 | | sdj | 0.02 | 0.00 | 0.01 | 0.01 | | sdk | 0.02 | 0.00 | 0.01 | 0.01 | | sdl | 0.17 | 0.20 | 0.17 | 0.18 | | sdm | 0.17 | 0.20 | 0.17 | 0.18 | This issue was originally discussed [1] when we first merged HST, and this patch was left as a low hanging fruit to be solved later. Regarding the implementation, as suggested by Mike in that mail thread, in order to avoid the overhead of ktime_get_ns for other selectors, this patch adds a flag for the selector code to request the high-resolution timer. I tested this using the same benchmark used in the original HST submission. Full test and benchmark scripts are available here: https://people.collabora.com/~krisman/HST-BIO-MPATH/ [1] https://lore.kernel.org/lkml/85tv0am9de.fsf@collabora.com/T/ Signed-off-by: Gabriel Krisman Bertazi [snitzer: cleaned up various implementation details] Signed-off-by: Mike Snitzer

dm mpath: pass IO start time to path selector

2020-05-15T14:29:36Z

The HST path selector needs this information to perform path prediction. For request-based mpath, struct request's io_start_time_ns is used, while for bio-based, use the start_time stored in dm_io. Signed-off-by: Gabriel Krisman Bertazi Signed-off-by: Mike Snitzer

dm path selector: remove 'repeat_count' return from .select_path hook

2016-02-23T03:34:42Z

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

dm mpath: add start_io and nr_bytes to path selectors

2009-06-22T09:12:27Z

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 Signed-off-by: Kiyoshi Ueda Signed-off-by: Jun'ichi Nomura Signed-off-by: Alasdair G Kergon

[PATCH] struct path: rename DM's struct path

2006-12-08T16:28:40Z

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 Acked-by: Alasdair G Kergon Cc: Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Linux-2.6.12-rc2

2005-04-16T22:20:36Z

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!