Hi Qlogic folks,
A question for you below..
On Sat, 2014-05-24 at 00:43 +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
>
> This patch converts qla2xxx target code to use generic percpu_ida
> tag allocation provided by target-core, thus removing the original
> kmem_cache_zalloc() for each struct qla_tgt_cmd descriptor in the
> incoming ATIO packet fast-path.
>
> This includes the conversion of qlt_handle_cmd_for_atio() to perform
> qla_tgt_sess lookup before dispatching a command descriptor into
> qla_tgt_wq process context, along with handling the case where no
> active session exists, and subsequently kicking off a seperate
> process context for qlt_create_sess_from_atio() to create a new one.
>
> It also includes moving tag allocation into generic code within
> qlt_get_tag(), so that the same logic can be shared between
> qlt_handle_cmd_for_atio() + qlt_create_sess_from_atio() contexts.
> Also, __qlt_do_work() has been made generic between both normal
> process context in qlt_do_work() + qlt_create_sess_from_atio().
>
> Next, update qlt_free_cmd() to release the percpu-ida tags, and
> drop the now-unused global qla_tgt_cmd_cachep.
>
> Finally in tcm_qla2xxx code, tcm_qla2xxx_check_initiator_node_acl()
> has been updated to use transport_init_session_tags() along with a
> hardcoded TCM_QLA2XXX_DEFAULT_TAGS=512 as the number of qla_tgt_cmd
> descriptors to pre-allocate per qla_tgt_sess instance.
>
> Cc: Saurav Kashyap <saurav.kashyap@xxxxxxxxxx>
> Cc: Quinn Tran <quinn.tran@xxxxxxxxxx>
> Cc: Giridhar Malavali <giridhar.malavali@xxxxxxxxxx>
> Cc: Chad Dupuis <chad.dupuis@xxxxxxxxxx>
> Cc: Roland Dreier <roland@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
> ---
> drivers/scsi/qla2xxx/qla_target.c | 195 ++++++++++++++++++++++++------------
> drivers/scsi/qla2xxx/qla_target.h | 6 ++
> drivers/scsi/qla2xxx/tcm_qla2xxx.c | 4 +-
> drivers/scsi/qla2xxx/tcm_qla2xxx.h | 2 +
> 4 files changed, 142 insertions(+), 65 deletions(-)
>
<SNIP>
> diff --git a/drivers/scsi/qla2xxx/tcm_qla2xxx.c b/drivers/scsi/qla2xxx/tcm_qla2xxx.c
> index 68fb66f..34db344 100644
> --- a/drivers/scsi/qla2xxx/tcm_qla2xxx.c
> +++ b/drivers/scsi/qla2xxx/tcm_qla2xxx.c
> @@ -1482,7 +1482,9 @@ static int tcm_qla2xxx_check_initiator_node_acl(
> }
> se_tpg = &tpg->se_tpg;
>
> - se_sess = transport_init_session(TARGET_PROT_NORMAL);
> + se_sess = transport_init_session_tags(TCM_QLA2XXX_DEFAULT_TAGS,
> + sizeof(struct qla_tgt_cmd),
> + TARGET_PROT_NORMAL);
> if (IS_ERR(se_sess)) {
> pr_err("Unable to initialize struct se_session\n");
> return PTR_ERR(se_sess);
> diff --git a/drivers/scsi/qla2xxx/tcm_qla2xxx.h b/drivers/scsi/qla2xxx/tcm_qla2xxx.h
> index 33aaac8..b0a3ea5 100644
> --- a/drivers/scsi/qla2xxx/tcm_qla2xxx.h
> +++ b/drivers/scsi/qla2xxx/tcm_qla2xxx.h
> @@ -4,6 +4,8 @@
> #define TCM_QLA2XXX_VERSION "v0.1"
> /* length of ASCII WWPNs including pad */
> #define TCM_QLA2XXX_NAMELEN 32
> +/* Number of pre-allocated per-session tags */
> +#define TCM_QLA2XXX_DEFAULT_TAGS 512
>
So a question wrt to the TCM_QLA2XXX_DEFAULT_TAGS value above used to
determine the number of qla_tgt_cmd descriptors to pre-allocate at
qla_tgt_sess creation time..
This value needs to line up with the total number of possible incoming
ATIO packets, plus the number of qla_tgt_cmd descriptors that have not
been acknowledged with a CTIO packet. Typically with other fabrics that
have been converted to use percpu_ida, we over-allocate the number of
per-session tags in order to completely avoid the slow-path where
percpu_ida has to steal tags from another CPU.
AFAICT, there is no way at the qla_target driver level to enforce
per-session queue_depth + reflect the depth at the initiator port, so
the number of tags needs to be the worst case number of HW descriptors
that a single session can consume + number of unacknowledged
descriptors.
So the question is, is there already a define somewhere in qla2xxx code
that TCM_QLA2XXX_DEFAULT_TAGS can use as a starting point..? If not,
what is the total number of outstanding commands that a single session
(or single port..?) can expect to handle at a given time..?
--nab
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