Re: kernel_lock() profiling results

[Manfred Spraul <manfreds@colorfullife.com>]

"Stephen C. Tweedie" wrote:
>         ftp://ftp.uk.linux.org/pub/linux/sct/performance
> 
> contains a patch Dave Miller and I put together to drop the kernel lock
> during a number of key user mode copies.

1) Andrea noticed that 'unlock_kernel()' only releases the kernel lock
if the lock was obtained once.
He added two new functions: one stores the current lock depth,
releases the lock and sets current->lock_depth =-1.
The other reverses that.

I think we need these functions:
* it's save to call the functions without the kernel_lock held.
* the unlock is effective for recursive calls.

2) Here's a excerpt from an email I wrote a few days ago:
> I've modified uaccess.h, and I have now a list of all functions which
> called copy_to/from_user() for more than 512 bytes (apache, make clean;
> make fs; find /usr/bin)
> 
> * read_file_actor()
> * ext2_file_write()
> * block_read()
> * copy_mount_options()  << really rare
> * proc_file_read()      << rare??
> * pipe_write()
> * pipe_read()
> * 2*vt_ioctl() << could be remote gdb.
> * tcp_do_sendmsg()
> * copy_strings()        << only during fork()?
> 
> Additionally, the following functions could also release the kernel
> lock:
> * padzero() in binfmt_elf:
>         This function clears up to 4096 bytes user memory.
>         The average should be 2048.
> * update_vm_mapping():
>         the function can wait in wait_on_page(), we should break nothing
> * get_free_page():
>         if GFP_WAIT, for memset(,0,PAGE_SIZE)
I didn't use NFS, knfsd, other fs except ext2.

--
	Manfred
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