On 07/17/2015 10:28 AM, Odzioba, Lukasz wrote:
From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx]
On Friday, July 17, 2015 6:55 PM Guenter Roeck wrote:
You don't really explain why your approach would be better than
allocating an array of pointers to struct temp_data and increasing
its size using krealloc if needed.
Let's consider two cases of such implementation:
a) we use array of pointers with O(n) access algorithm
b) we use array of pointers with O(1) access algorithm
In both cases an array will have greater memory footprint unless
we implement reallocation ourselves when cpus are disabled which will
make code harder to maintain.
Please explain why krealloc() won't work, why using krealloc(()
would result in a larger memory footprint than using lists,
and why disabling CPUs would require any action in the first place.
Case b) does not handle huge core ids and sparse enumeration well -
it is still to discuss whether we really need it since there is no
such hardware yet.
"yet" is a key term here. Presumably you have insider information.
Unless you can share this information, I don't see the point of
replacing an O(1) algorithm with O(n), especially since there
is a relatively simple alternative available to support more CPUs.
I am not saying that my solution is the best of possible ones.
I am saying that "the best" can vary depending on which criteria do you
choose from (time, memory, clean code...). Some may say that O(n) is
fine unless we have thousands of cores and this code is not on hot path,
others may be concerned more about memory on small/old devices.
I don't see holy grail here, If you see one please let me know.
Unless you clarify that Intel will introduce CPU IDs which can not be used
as array index because they are too sparse, I don't really see how the list
solution would consume less memory than an array of pointers, even if the
array is somewhat sparse. After all, a list consumes at least two pointers
per entry.
Thanks,
Guenter
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