Re: [PATCH v2 00/11] usb: gadget: reduce usb gadget trace event buffer usage

[Linyu Yuan <quic_linyyuan@quicinc.com>]

On 9/11/2023 9:32 PM, Greg Kroah-Hartman wrote:
> On Mon, Sep 11, 2023 at 07:24:35PM +0800, Linyu Yuan wrote:
>> some trace event use an interger to to save a bit field info of gadget,
>> also some trace save endpoint name in string forat, it all can be
>> chagned to other way at trace event store phase.
>>
>> bit field can be replace with a union interger member which include
>> multiple bit fields.
>>
>> ep name stringe can be replace to a interger which contaion number
>> and dir info.
> Ok, but how much memory did you actually save here?  Is the memory saved
> only if tracing is enbaled, or it is always?  Is there a speed penality
> for these changes or is it the same?

yes, it is save trace ring buffer only when tracing enabled, as save 
less data, speed is higher.


it is help when enable trace for a long period.


for a single trace entry, take struct usb_gadget as example, at worst 
case, it save (19 dword  - 1 dword) / 19dword = 94% buffer.


for ep name, it only need 4 bytes/  (4bytes + 9bytes ) = 30%.


>
> You are doing a lot of code reorginization without any real explaination
> of why this is needed, nor proof about it.
>
> thanks,
>
> greg k-h