> On 3. 8. 2023, at 13:34, Vinod Koul <vkoul@xxxxxxxxxx> wrote:
>
> On 03-08-23, 10:32, Martin Povišer wrote:
>
>>>>> +static int sio_alloc_tag(struct sio_data *sio)
>>>>> +{
>>>>> + struct sio_tagdata *tags = &sio->tags;
>>>>> + int tag, i;
>>>>> +
>>>>> + /*
>>>>> + * Because tag number 0 is special, the usable tag range
>>>>> + * is 1...(SIO_NTAGS - 1). So, to pick the next usable tag,
>>>>> + * we do modulo (SIO_NTAGS - 1) *then* plus one.
>>>>> + */
>>>>> +
>>>>> +#define SIO_USABLE_TAGS (SIO_NTAGS - 1)
>>>>> + tag = (READ_ONCE(tags->last_tag) % SIO_USABLE_TAGS) + 1;
>>>>> +
>>>>> + for (i = 0; i < SIO_USABLE_TAGS; i++) {
>>>>> + if (!test_and_set_bit(tag, &tags->allocated))
>>>>> + break;
>>>>> +
>>>>> + tag = (tag % SIO_USABLE_TAGS) + 1;
>>>>> + }
>>>>> +
>>>>> + WRITE_ONCE(tags->last_tag, tag);
>>>>> +
>>>>> + if (i < SIO_USABLE_TAGS)
>>>>> + return tag;
>>>>> + else
>>>>> + return -EBUSY;
>>>>> +#undef SIO_USABLE_TAGS
>>>>> +}
>>>>
>>>> can you use kernel mechanisms like ida to alloc and free the tags...
>>>
>>> I can look into that.
>>
>> Documentation says IDA is deprecated in favour of Xarray, both look
>> like they serve to associate a pointer with an ID. I think neither
>> structure beats a simple bitfield and a static array for the per-tag
>> data. Agree?
>
> yeah xarray am not too sure. I would still go with ida, we will see when
> it is relly removed.
Sorry for letting this sleep for a while.
I don’t like the idea of submitting a new driver to use a deprecated
interface. For all I know someone can come along later and mark the driver
as broken in the process of finally removing IDA, with good excuse to do so.
> If you need a bitfield why not use bitmap apis.
> I dont like drivers implementing the basic logic which kernel provides
I think one improvement to take up is to use the DECLARE_BITMAP macro for
the `allocated` bitmap. Other than that this already uses the bitmap.h/
bitops.h functions to the degree it can if the goal is to
(1) allocate and free the tags reliably under SMP with atomic ops
(2) in best-effort manner (but without locking of the counter) make
the tag numbers consecutive
The latter behaviour is there to make traces easier to read.
Martin
> --
> ~Vinod
