| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <2f94f241-445f-1beb-c4a8-73f6efce5af2@huaweicloud.com>
Date: Wed, 27 Jul 2022 20:11:14 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Paolo VALENTE <paolo.valente@...more.it>
Cc: Jan Kara <jack@...e.cz>, cgroups@...r.kernel.org,
linux-block <linux-block@...r.kernel.org>,
Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
LKML <linux-kernel@...r.kernel.org>, yi.zhang@...wei.com,
"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next v10 3/4] block, bfq: refactor the counting of
'num_groups_with_pending_reqs'
Hi, Paolo
Are you still interested in this patchset?
在 2022/07/20 19:38, Yu Kuai 写道:
> Hi
>
> 在 2022/07/20 19:24, Paolo VALENTE 写道:
>>
>>
>>> Il giorno 12 lug 2022, alle ore 15:30, Yu Kuai
>>> <yukuai1@...weicloud.com <mailto:yukuai1@...weicloud.com>> ha scritto:
>>>
>>> Hi!
>>>
>>> I'm copying my reply with new mail address, because Paolo seems
>>> didn't receive my reply.
>>>
>>> 在 2022/06/23 23:32, Paolo Valente 写道:
>>>> Sorry for the delay.
>>>>> Il giorno 10 giu 2022, alle ore 04:17, Yu Kuai <yukuai3@...wei.com
>>>>> <mailto:yukuai3@...wei.com>> ha scritto:
>>>>>
>>>>> Currently, bfq can't handle sync io concurrently as long as they
>>>>> are not issued from root group. This is because
>>>>> 'bfqd->num_groups_with_pending_reqs > 0' is always true in
>>>>> bfq_asymmetric_scenario().
>>>>>
>>>>> The way that bfqg is counted into 'num_groups_with_pending_reqs':
>>>>>
>>>>> Before this patch:
>>>>> 1) root group will never be counted.
>>>>> 2) Count if bfqg or it's child bfqgs have pending requests.
>>>>> 3) Don't count if bfqg and it's child bfqgs complete all the
>>>>> requests.
>>>>>
>>>>> After this patch:
>>>>> 1) root group is counted.
>>>>> 2) Count if bfqg have pending requests.
>>>>> 3) Don't count if bfqg complete all the requests.
>>>>>
>>>>> With this change, the occasion that only one group is activated
>>>>> can be
>>>>> detected, and next patch will support concurrent sync io in the
>>>>> occasion.
>>>>>
>>>>> Signed-off-by: Yu Kuai <yukuai3@...wei.com
>>>>> <mailto:yukuai3@...wei.com>>
>>>>> Reviewed-by: Jan Kara <jack@...e.cz <mailto:jack@...e.cz>>
>>>>> ---
>>>>> block/bfq-iosched.c | 42 ------------------------------------------
>>>>> block/bfq-iosched.h | 18 +++++++++---------
>>>>> block/bfq-wf2q.c | 19 ++++---------------
>>>>> 3 files changed, 13 insertions(+), 66 deletions(-)
>>>>>
>>>>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>>>>> index 0ec21018daba..03b04892440c 100644
>>>>> --- a/block/bfq-iosched.c
>>>>> +++ b/block/bfq-iosched.c
>>>>> @@ -970,48 +970,6 @@ void __bfq_weights_tree_remove(struct
>>>>> bfq_data *bfqd,
>>>>> void bfq_weights_tree_remove(struct bfq_data *bfqd,
>>>>> struct bfq_queue *bfqq)
>>>>> {
>>>>> -struct bfq_entity *entity = bfqq->entity.parent;
>>>>> -
>>>>> -for_each_entity(entity) {
>>>>> -struct bfq_sched_data *sd = entity->my_sched_data;
>>>>> -
>>>>> -if (sd->next_in_service || sd->in_service_entity) {
>>>>> -/*
>>>>> -* entity is still active, because either
>>>>> -* next_in_service or in_service_entity is not
>>>>> -* NULL (see the comments on the definition of
>>>>> -* next_in_service for details on why
>>>>> -* in_service_entity must be checked too).
>>>>> -*
>>>>> -* As a consequence, its parent entities are
>>>>> -* active as well, and thus this loop must
>>>>> -* stop here.
>>>>> -*/
>>>>> -break;
>>>>> -}
>>>>> -
>>>>> -/*
>>>>> -* The decrement of num_groups_with_pending_reqs is
>>>>> -* not performed immediately upon the deactivation of
>>>>> -* entity, but it is delayed to when it also happens
>>>>> -* that the first leaf descendant bfqq of entity gets
>>>>> -* all its pending requests completed. The following
>>>>> -* instructions perform this delayed decrement, if
>>>>> -* needed. See the comments on
>>>>> -* num_groups_with_pending_reqs for details.
>>>>> -*/
>>>>> -if (entity->in_groups_with_pending_reqs) {
>>>>> -entity->in_groups_with_pending_reqs = false;
>>>>> -bfqd->num_groups_with_pending_reqs--;
>>>>> -}
>>>>> -}
>>>> With this part removed, I'm missing how you handle the following
>>>> sequence of events:
>>>> 1. a queue Q becomes non busy but still has dispatched requests, so
>>>> it must not be removed from the counter of queues with pending reqs
>>>> yet
>>>> 2. the last request of Q is completed with Q being still idle (non
>>>> busy). At this point Q must be removed from the counter. It seems to
>>>> me that this case is not handled any longer
>>> Hi, Paolo
>>>
>>> 1) At first, patch 1 support to track if bfqq has pending requests,
>>> it's
>>> done by setting the flag 'entity->in_groups_with_pending_reqs' when the
>>> first request is inserted to bfqq, and it's cleared when the last
>>> request is completed(based on weights_tree insertion and removal).
>>>
>>
>> In patch 1 I don't see the flag cleared for the request-completion
>> event :(
>>
>> The piece of code involved is this:
>>
>> static void bfq_completed_request(struct bfq_queue *bfqq, struct
>> bfq_data *bfqd)
>> {
>> u64 now_ns;
>> u32 delta_us;
>>
>> bfq_update_hw_tag(bfqd);
>>
>> bfqd->rq_in_driver[bfqq->actuator_idx]--;
>> bfqd->tot_rq_in_driver--;
>> bfqq->dispatched--;
>>
>> if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
>> /*
>> * Set budget_timeout (which we overload to store the
>> * time at which the queue remains with no backlog and
>> * no outstanding request; used by the weight-raising
>> * mechanism).
>> */
>> bfqq->budget_timeout = jiffies;
>>
>> bfq_weights_tree_remove(bfqd, bfqq);
>> }
>> ...
>>
>> Am I missing something?
>
> I add a new api bfq_del_bfqq_in_groups_with_pending_reqs() in patch 1
> to clear the flag, and it's called both from bfq_del_bfqq_busy() and
> bfq_completed_request(). I think you may miss the later:
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 0d46cb728bbf..0ec21018daba 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -6263,6 +6263,7 @@ static void bfq_completed_request(struct
> bfq_queue *bfqq, struct bfq_data *bfqd)
> */
> bfqq->budget_timeout = jiffies;
>
> + bfq_del_bfqq_in_groups_with_pending_reqs(bfqq);
> bfq_weights_tree_remove(bfqd, bfqq);
> }
>
> Thanks,
> Kuai
>>
>> Thanks,
>> Paolo
Powered by blists - more mailing lists