[stgt] [PATCH RFC v2] tgtd: send/recv iSCSI PDUs in worker threads

[FUJITA Tomonori]

On Sun, 10 Nov 2013 17:49:07 +0900
Hitoshi Mitake <mitake.hitoshi at gmail.com> wrote:

> From: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> 
> Current tgtd sends and receives iSCSI PDUs in its main event
> loop. This design can cause bottleneck when many iSCSI clients connect
> to single tgtd process. For example, we need multiple tgtd processes
> for utilizing fast network like 10 GbE because typical single
> processor core isn't fast enough for processing bunch of requests.
> 
> This patch lets tgtd send/receive iSCSI PDUs and check digests in its
> worker threads. After applying this patch, the bottleneck in the main
> event loop is removed and the performance is improved.
> 
> The improvement can be seen even if tgtd and iSCSI initiator are
> running on a single host. Below is a snippet of fio result on my
> laptop. The workload is 128MB random RW. Backingstore is sheepdog.
> 
> Original tgtd:
>   read : io=65392KB, bw=4445.2KB/s, iops=1111, runt= 14711msec
>   write: io=65680KB, bw=4464.8KB/s, iops=1116, runt= 14711msec
> 
> tgtd with this patch:
>   read : io=65392KB, bw=5098.9KB/s, iops=1274, runt= 12825msec
>   write: io=65680KB, bw=5121.3KB/s, iops=1280, runt= 12825msec
> 
> This change will be more effective when a number of iSCSI clients
> increases. I'd like to hear your comments on this change.
> 
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> ---
> 
> v2:
>  - correct handling of connection closing based on a reference count of an iSCSI
>    connection
>  - a silly bug in iscsi_tcp_init() introduced in the previous patch is removed
> 
>  usr/iscsi/conn.c      |  12 ++-
>  usr/iscsi/iscsi_tcp.c | 293 +++++++++++++++++++++++++++++++++++++++++++++++---
>  usr/iscsi/iscsid.c    |  61 +++++++----
>  usr/iscsi/iscsid.h    |   8 +-
>  4 files changed, 334 insertions(+), 40 deletions(-)

This can handle a single iscsi session having multiple tcp
connections? For example, if iscsi_scsi_cmd_rx_start() is called by
multiple threads, conn->session->cmd_list is accessed by them without
a lock?


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