Re: staging: r8188eu: how to handle nested mutex under spinlock

[Pavel Skripkin <paskripkin@gmail.com>]

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Hi David,

On 4/4/22 19:59, David Laight wrote:
> From: Pavel Skripkin
>> Sent: 04 April 2022 17:39
>> 
>> Hi David,
>> 
>> On 4/4/22 11:50, David Laight wrote:
>> >>
>> >> > 		while (pwrpriv->bInSuspend &&
>> >>
>> >> I've looked into what gcc11 produced from this function and looks like
>> >> my compiler is smart enough to not cache that value, but I am afraid not
>> >> all compilers are that smart.
>> >
>> > The compiler can't cache the value because of the function call.
>> >
>> 
>> Hm, I am a newbie in compilers, so can you, please, explain (or give a
>> link to any resource where I can read about it) how function call here
>> prevent caching.
>> 
>> IIUC compiler generates code that works well in scope of single-threaded
>> application, so why can't compiler cache that value instead of accessing
>> memory on each iteration... Isn't register access a way faster than even
>> cache hit?
> 
> Because calls to external functions are allowed to change
> any data via 'other' references.
> For instance the structure pointer the function has could
> also be in global data somewhere.
> 

Make sense, thank you for explanation!




With regards,
Pavel Skripkin

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