blk_iopoll_enabled

blk_iopoll_enabled

[Sagi Grimberg]

Hey Jens,

So I'm looking at blk_iopoll for iSER & SRP and I have one gap I would 
like to get your input on.

In blk-iopoll.c I see:
int blk_iopoll_enabled = 1;
EXPORT_SYMBOL(blk_iopoll_enabled);

This is set to 1 and exported for everyone to condition and *modify* it.
The documentation says the user must check this when using blk_iopoll.

My question is why? it should always be true shouldn't it?
Moreover, isn't it better to protect it using a get() function of it?
can't someone set it to 0 and shutdown the lights on everyone else?

Thanks,

Sagi.

Re: blk_iopoll_enabled

[Jens Axboe]

On 2014-03-12 11:35, Sagi Grimberg wrote:
> Hey Jens,
>
> So I'm looking at blk_iopoll for iSER & SRP and I have one gap I would
> like to get your input on.
>
> In blk-iopoll.c I see:
> int blk_iopoll_enabled = 1;
> EXPORT_SYMBOL(blk_iopoll_enabled);
>
> This is set to 1 and exported for everyone to condition and *modify* it.
> The documentation says the user must check this when using blk_iopoll.
>
> My question is why? it should always be true shouldn't it?
> Moreover, isn't it better to protect it using a get() function of it?
> can't someone set it to 0 and shutdown the lights on everyone else?

We can kill it. IIRC, it was mostly used during development to test 
functionality and performance (and wired to a sysfs toggle file).

But... Just because it's exported doesn't mean that random users are 
allowed to just disable it. What's left now is an always-on, so we can 
remove it.

-- 
Jens Axboe

Re: blk_iopoll_enabled

[Jens Axboe]

On 03/12/2014 09:40 PM, Jens Axboe wrote:
> On 2014-03-12 11:35, Sagi Grimberg wrote:
>> Hey Jens,
>>
>> So I'm looking at blk_iopoll for iSER & SRP and I have one gap I would
>> like to get your input on.
>>
>> In blk-iopoll.c I see:
>> int blk_iopoll_enabled = 1;
>> EXPORT_SYMBOL(blk_iopoll_enabled);
>>
>> This is set to 1 and exported for everyone to condition and *modify* it.
>> The documentation says the user must check this when using blk_iopoll.
>>
>> My question is why? it should always be true shouldn't it?
>> Moreover, isn't it better to protect it using a get() function of it?
>> can't someone set it to 0 and shutdown the lights on everyone else?
>
> We can kill it. IIRC, it was mostly used during development to test
> functionality and performance (and wired to a sysfs toggle file).
>
> But... Just because it's exported doesn't mean that random users are
> allowed to just disable it. What's left now is an always-on, so we can
> remove it.

It _is_ still exported, I just forgot it was put in sysctl. I'll kill it 
off completely now. It's safe to toggle from user space, but only 
practically so if IO is idle. It makes no attempt to ensure that, as it 
was just a debug thing.

-- 
Jens Axboe

Re: blk_iopoll_enabled

[Sagi Grimberg]

On 3/13/2014 5:34 PM, Jens Axboe wrote:
> On 03/12/2014 09:40 PM, Jens Axboe wrote:
>> On 2014-03-12 11:35, Sagi Grimberg wrote:
>>> Hey Jens,
>>>
>>> So I'm looking at blk_iopoll for iSER & SRP and I have one gap I would
>>> like to get your input on.
>>>
>>> In blk-iopoll.c I see:
>>> int blk_iopoll_enabled = 1;
>>> EXPORT_SYMBOL(blk_iopoll_enabled);
>>>
>>> This is set to 1 and exported for everyone to condition and *modify* 
>>> it.
>>> The documentation says the user must check this when using blk_iopoll.
>>>
>>> My question is why? it should always be true shouldn't it?
>>> Moreover, isn't it better to protect it using a get() function of it?
>>> can't someone set it to 0 and shutdown the lights on everyone else?
>>
>> We can kill it. IIRC, it was mostly used during development to test
>> functionality and performance (and wired to a sysfs toggle file).
>>
>> But... Just because it's exported doesn't mean that random users are
>> allowed to just disable it. What's left now is an always-on, so we can
>> remove it.
>
> It _is_ still exported, I just forgot it was put in sysctl. I'll kill 
> it off completely now. It's safe to toggle from user space, but only 
> practically so if IO is idle. It makes no attempt to ensure that, as 
> it was just a debug thing.
>

Thanks

Sagi.