[dm-devel] DM-Delay

[BK, GirishKumar]

Hi Vasily,

It would great if you could point us to your sample code which uses
high-res timers.
We hope to add delays in the range of 20 - 500 u sec in dm-cache path.

Thanks,
/Girish BK


On 1/22/15, 8:42 PM, "Vasily Tarasov" <tarasov at vasily.name> wrote:

>Hi Sourav,
>
>Delay target provides uniform latency with 1ms granularity. You can
>specify different latency for reads or writes. No matter what is the
>size of the request or the number of requests submitted - the delay
>will remain the same.
>
>To change granularity to microseconds the code need to be modified to
>use high-res timers (instead of regular Linux timers). It is
>relatively straight forward modification,  I did it once and have a
>patch somewhere. Let me see if I can find it.
>
>HTH,
>Vasily
>
>On Wed, Jan 21, 2015 at 12:15 PM, Sourav Basu <sourav.juit at gmail.com>
>wrote:
>> Hello,
>>    I have few questions regarding dm-delay component.
>> 1. Why type of emulations is targeted while implementation of dm-delay?
>>  2. Is the delay uniform across different i/o going to the device?
>>  3. Can the granularity of be reduced from mili-sec to tens of
>>micro-sec? If
>> so how?
>>
>> My aim is to emulate ssd devices latency varying from 10us to 100ms on
>> ramdisk using dm-delay.
>>
>> Regards,
>> Sourav
>>
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