"I don't understand how you would prefetch this page from the kernel
space"
"
My means is not prefetch the page but use prefetch instruction
(e.g. __asm__ __volatile__( " prefetchnta %0" : : "m" (*addr) ) ;// addr is
fist parameter of pagefault handler, which caused page fault trap), prefetch
the content in the addr into cache line.
" The page is mapped into the application's address space, not the
kernel's. There is no mechanism to prefetch a page that isn't mapped
into the address space of the executing context"
Yes, I agree with you.
for example:
1.fd=open("/var/tmp/mmap.file",O_RDWR);
2. volatile unsigned char* s=mmap(,,,,fd,0L);
3.a =s[4096];
the step 3 will cause pagefault trap, before returning to user space from
pagefault handler, we may use prefetch instruction to load the data into cache
line inadvance
"As a further wrinkle, there's no guarantee that when you return from the
pagefault trap you'll be executing the application that caused the
pagefault. trap_rtt() makes a call to preempt(), scheduling a
different process on CPU.
"
Yes I agree with you, it is possible sometimes.
Thanks,
Ma Ling
[EMAIL PROTECTED] wrote:
> "The user program would have trouble
> doing the prefetch,
> because it is often difficult to predict
> where page faults will happen
> and because a prefetch before
> the page fault will probably have no effect.
> "
>
> The prefetch instruciton will execute in kernel space.
>
>
>
> we add prefetch instruciton in pagefault handler after successfully
> geting physical memory ,becasuse we know the user programe will soon
> access the address again.
I don't understand how you would prefetch this page from the kernel
space. The page is mapped into the application's address space, not the
kernel's. There is no mechanism to prefetch a page that isn't mapped
into the address space of the executing context.
As a further wrinkle, there's no guarantee that when you return from the
pagefault trap you'll be executing the application that caused the
pagefault. trap_rtt() makes a call to preempt(), scheduling a
different process on CPU.
-j
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