[PATCH RFC 0/2] percpu_tags: Prototype implementation
From: Alexander Gordeev
Date: Fri Jul 18 2014 - 06:20:33 EST
Hello Gentleman,
This is a development of "percpu_ida" library. I named it
"percpu_tags" to simplify review, since most of "percpu_ida"
code has gone and a diff would not be informative.
While the concept of per-cpu arrays is is preserved, the
implementation is heavily reworked. The main objective is to
improve the "percpu_ida" locking scheme.
Here is the list of major differrences between "percpu_ida" and
"percpu_tags":
* The global freelist has gone. As result, CPUs do not compete
for the global lock.
* Long-running operatons (scanning thru a cpumask) are executed
with local interrupts enabled;
* percpu_ida::percpu_max_size limit is eliminated. Instead, the
limit is determined dynamically. Depending from how many CPUs
are requesting tags each CPU gets a fair share of the tag space;
* A tag is attempted to return to the CPU it was allocated on. As
result, it is expected the locality of data associated with the
tag benefits;
The code is largely raw and untested. The reason I am posting
is the prototype implementation performs 2-3 times faster than
"percpu_ida", so I would like to ensure if it worth going further
with this approach or is there a no-go.
The performance test is not decent, though. I used "fio" random
read against a "null_blk" device sitting on top of "percpu_tags",
which is not exactly how "percpu_ida" is used. This is another
reason I am posting - an advice on how to properly test is very
appreciated.
The source code could be found at
https://github.com/a-gordeev/linux.git percpu_tags-v0
Thanks!
Cc: linux-scsi@xxxxxxxxxxxxxxx
Cc: qla2xxx-upstream@xxxxxxxxxx
Cc: Nicholas Bellinger <nab@xxxxxxxxxxxxx>
Cc: Kent Overstreet <kmo@xxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Alexander Gordeev (2):
percpu_tags: Prototype implementation
percpu_tags: Use percpu_tags instead of percpu_ida
drivers/scsi/qla2xxx/qla_target.c | 6 +-
drivers/target/iscsi/iscsi_target_util.c | 6 +-
drivers/target/target_core_transport.c | 4 +-
drivers/target/tcm_fc/tfc_cmd.c | 8 +-
drivers/vhost/scsi.c | 6 +-
include/linux/percpu_tags.h | 37 ++
include/target/target_core_base.h | 4 +-
lib/Makefile | 2 +-
lib/percpu_tags.c | 556 ++++++++++++++++++++++++++++++
9 files changed, 611 insertions(+), 18 deletions(-)
create mode 100644 include/linux/percpu_tags.h
create mode 100644 lib/percpu_tags.c
--
1.7.7.6
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