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SubjectRe: Patch 2/9] Initialization
Jes Sorensen wrote:

>>>>>>"Shailabh" == Shailabh Nagar <> writes:
>Shailabh> delayacct-setup.patch Initialization code related to
>Shailabh> collection of per-task "delay" statistics which measure how
>Shailabh> long it had to wait for cpu, sync block io, swapping
>Shailabh> etc. The collection of statistics and the interface are in
>Shailabh> other patches. This patch sets up the data structures and
>Shailabh> allows the statistics collection to be disabled through a
>Shailabh> kernel boot paramater.
>Shailabh> +#ifdef CONFIG_TASK_DELAY_ACCT
>Shailabh> +struct task_delay_info {
>Shailabh> + spinlock_t lock;
>Shailabh> +
>Shailabh> + /* For each stat XXX, add following, aligned appropriately
>Shailabh> + *
>Shailabh> + * struct timespec XXX_start, XXX_end;
>Shailabh> + * u64 XXX_delay;
>Shailabh> + * u32 XXX_count;
>Shailabh> + */
>Shailabh> +};
>Shailabh> +#endif
>I thought you were going to change this to do
>u64 some_delay
>u32 foo_count
>u32 bar_count
>u64 another_delay
>To avoid wasting space on 64 bit platforms.

Well, the "aligned appropriately" part of the comment was intended to let
future users know that something like the above should be done.

e.g in a subsequent patch (5/9)
when we introduce the additional stat swapin_delay/count, a 64-bit friendly
alignment is being done thus:

u64 blkio_delay; /* wait for sync block io completion */
+ u64 swapin_delay; /* wait for sync block io completion */
u32 blkio_count;
+ u32 swapin_count;

The need for each stat, potentially, to need a separate set of timespec
to reduce nesting problems does introduce another wrinkle in
since you'd ideally like to have all the XXX_* variables close together.
Right now
we're good since swapin doesn't need extra timespecs of its own. But future
additions might need to be more careful.



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