2023-03-30 13:11:53

by Avri Altman

Subject: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

in UFS, each request is designated via the triplet <iid, lun, task tag>.

In UFS4.0 the Initiator ID field is 8 bits wide, comprised of the
EXT_IID and IID fields. Together with the task tag (single byte), they
limit the driver's hw queues capacity.

Signed-off-by: Avri Altman <[email protected]>
---
drivers/ufs/core/ufshcd.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 35a3bd95c5e4..d529c42a682a 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -8468,6 +8468,10 @@ static int ufshcd_alloc_mcq(struct ufs_hba *hba)
if (ret)
goto err;

+ if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
+ "there can be at most 1<<16 inflight requests\n"))
+ goto err;
+
/*
* Previously allocated memory for nutrs may not be enough in MCQ mode.
* Number of supported tags in MCQ mode may be larger than SDB mode.
--
2.17.1

2023-03-30 14:17:28

by Johannes Thumshirn

Subject: Re: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

On 30.03.23 15:11, Avri Altman wrote:
> + if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
> + "there can be at most 1<<16 inflight requests\n"))
> + goto err;

Hmm why not SZ_64K - 1?

2023-03-30 16:40:34

by Bart Van Assche

Subject: Re: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

On 3/30/23 06:11, Avri Altman wrote:
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 35a3bd95c5e4..d529c42a682a 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -8468,6 +8468,10 @@ static int ufshcd_alloc_mcq(struct ufs_hba *hba)
> if (ret)
> goto err;
>
> + if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
> + "there can be at most 1<<16 inflight requests\n"))
> + goto err;
> +
> /*
> * Previously allocated memory for nutrs may not be enough in MCQ mode.
> * Number of supported tags in MCQ mode may be larger than SDB mode.

Hi Avri,

WARN*() should only be used to report kernel bugs. hba->nutrs *
hba->nr_hw_queues being too large is not a kernel bug but a
configuration issue.

Instead of failing MCQ allocation, shouldn't
ufshcd_mcq_decide_queue_depth() be modified such that it restricts
hba->nutrs to a value that can be supported?

Thanks,

Bart.

2023-03-30 18:37:28

by Avri Altman

Subject: RE: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

> On 30.03.23 15:11, Avri Altman wrote:
> > + if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
> > + "there can be at most 1<<16 inflight requests\n"))
> > + goto err;
>
> Hmm why not SZ_64K - 1?
But of course.

Thanks,
Avri

2023-03-30 18:42:33

by Avri Altman

Subject: RE: [PATCH] scsi: ufs: mcq: Limit the amount of inflight requests

> On 3/30/23 06:11, Avri Altman wrote:
> > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> > index 35a3bd95c5e4..d529c42a682a 100644
> > --- a/drivers/ufs/core/ufshcd.c
> > +++ b/drivers/ufs/core/ufshcd.c
> > @@ -8468,6 +8468,10 @@ static int ufshcd_alloc_mcq(struct ufs_hba *hba)
> > if (ret)
> > goto err;
> >
> > + if (WARN_ONCE(hba->nutrs * hba->nr_hw_queues > (1 << 16) - 1,
> > + "there can be at most 1<<16 inflight requests\n"))
> > + goto err;
> > +
> > /*
> > * Previously allocated memory for nutrs may not be enough in MCQ
> mode.
> > * Number of supported tags in MCQ mode may be larger than SDB
> mode.
>
> Hi Avri,
>
> WARN*() should only be used to report kernel bugs. hba->nutrs *
> hba->nr_hw_queues being too large is not a kernel bug but a
> configuration issue.
Will replace with an appropriate dev_info and a clarifying comment.

>
> Instead of failing MCQ allocation, shouldn't
> ufshcd_mcq_decide_queue_depth() be modified such that it restricts
> hba->nutrs to a value that can be supported?
The driver's capacity is the product of hba->nutrs * hba->nr_hw_queues,
Where the latter is being established only later in ufshcd_mcq_init.

Thanks,
Avri
>
> Thanks,
>
> Bart.