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SubjectRe: [PATCH 1/2] Convert target drivers to use sbitmap
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On 5/15/18 10:11 AM, Jens Axboe wrote:
> On 5/15/18 10:00 AM, Matthew Wilcox wrote:
>> From: Matthew Wilcox <mawilcox@microsoft.com>
>>
>> The sbitmap and the percpu_ida perform essentially the same task,
>> allocating tags for commands. Since the sbitmap is more used than
>> the percpu_ida, convert the percpu_ida users to the sbitmap API.
>
> It should also be the same performance as percpu_ida in light use, and
> performs much better at > 50% utilization of the tag space. I think
> that's better justification than "more used than".
>
>> diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
>> index 4435bf374d2d..28bcffae609f 100644
>> --- a/drivers/target/iscsi/iscsi_target_util.c
>> +++ b/drivers/target/iscsi/iscsi_target_util.c
>> @@ -17,7 +17,7 @@
>> ******************************************************************************/
>>
>> #include <linux/list.h>
>> -#include <linux/percpu_ida.h>
>> +#include <linux/sched/signal.h>
>> #include <net/ipv6.h> /* ipv6_addr_equal() */
>> #include <scsi/scsi_tcq.h>
>> #include <scsi/iscsi_proto.h>
>> @@ -147,6 +147,28 @@ void iscsit_free_r2ts_from_list(struct iscsi_cmd *cmd)
>> spin_unlock_bh(&cmd->r2t_lock);
>> }
>>
>> +int iscsit_wait_for_tag(struct se_session *se_sess, int state, int *cpup)
>> +{
>> + int tag = -1;
>> + DEFINE_WAIT(wait);
>> + struct sbq_wait_state *ws;
>> +
>> + if (state == TASK_RUNNING)
>> + return tag;
>> +
>> + ws = &se_sess->sess_tag_pool.ws[0];
>> + for (;;) {
>> + prepare_to_wait_exclusive(&ws->wait, &wait, state);
>> + if (signal_pending_state(state, current))
>> + break;
>> + schedule();
>> + tag = sbitmap_queue_get(&se_sess->sess_tag_pool, cpup);
>> + }
>> +
>> + finish_wait(&ws->wait, &wait);
>> + return tag;
>> +}
>
> Seems like that should be:
>
>
> ws = &se_sess->sess_tag_pool.ws[0];
> for (;;) {
> prepare_to_wait_exclusive(&ws->wait, &wait, state);
> if (signal_pending_state(state, current))
> break;
> tag = sbitmap_queue_get(&se_sess->sess_tag_pool, cpup);
> if (tag != -1)
> break;
> schedule();
> }
>
> finish_wait(&ws->wait, &wait);
> return tag;
>
>> /*
>> * May be called from software interrupt (timer) context for allocating
>> * iSCSI NopINs.
>> @@ -155,9 +177,11 @@ struct iscsi_cmd *iscsit_allocate_cmd(struct iscsi_conn *conn, int state)
>> {
>> struct iscsi_cmd *cmd;
>> struct se_session *se_sess = conn->sess->se_sess;
>> - int size, tag;
>> + int size, tag, cpu;
>>
>> - tag = percpu_ida_alloc(&se_sess->sess_tag_pool, state);
>> + tag = sbitmap_queue_get(&se_sess->sess_tag_pool, &cpu);
>> + if (tag < 0)
>> + tag = iscsit_wait_for_tag(se_sess, state, &cpu);
>> if (tag < 0)
>> return NULL;
>
> Might make sense to just roll the whole thing into iscsi_get_tag(), that
> would be cleaner.
>
> sbitmap should provide a helper for that, but we can do that cleanup
> later. That would encapsulate things like the per-cpu caching hint too,
> for instance.
>
> Rest looks fine to me.

Are you going to push this further? I really think we should.

--
Jens Axboe

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