Zhang, Yanmin wrote:
> struct task_delay_info is used by per process block I/O delay statistics
> feature which is useful in kernel. This struct is not optimized.
>
> My patch against kernel 2.6.22 shrinks it a half.
>
> 1) Delete blkio_start and blkio_end. As the collection happens in
> io_schedule and io_schedule_timeout, we use local variables to
> replace them;
I am not sure if it's a good idea to push items on the stack.
Remember we are moving to 4K stacks.
> 2) Delete lock. The change to the protected data has no nested cases.
> In addition, the result is for performance data collection, so it’s
> unnecessary to add such lock.
This is a cause of concern, we cannot afford to have incorrect data
collected. Incorrect/unreliable data which is worthless.
> 3) Delete flags. It just has one value. Use the most significant bit of
> blkio_delay (64 bits) to mark it..
>
Yes, thats true right now, but I am not sure if we should go optimize
that so early. We could end up adding other accounting/extending the
framework, we'll need to add the flags back then.
> -static inline void delayacct_clear_flag(int flag)
> +static inline void delayacct_clear_swapin(void)
> {
> if (current->delays)
> - current->delays->flags &= ~flag;
> + current->delays->blkio_delay |= DELAYACCT_PF_SWAPIN;
BTW, you should be clearing the flag here.
Overall, the lock removal is not acceptable. I don't like the bit
hacking for flags and moving counters to the stack either.
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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