* Eric Dumazet <[email protected]> wrote:
> O(1) lookup doesnt imply it needs to be super-fast. You make a
> confusion about this.
Davide has written many good speedups for the kernel and he is one of
the best scalability experts the Linux kernel has today. You could learn
from Davide a thing or two, instead of lecturing him about O(1) ...
For example, the recent futex.c changes you did in commit 34f01cc1 are,
and unfortunately there's no better word i can find: plain disgusting.
You apparently have plopped the 'fshared' code into the existing logic
via conditionals and have blown up the complexity of the functions for
no good reason - instead of neatly separating them out. You have added
_33_ (thirty-three!) new 'if' branches to futex.c! The feature you
introduced is nice and useful, but for heaven's sake please work on
cleanliness of your code some more and undo that colossal damage ...
preferably before working on other areas of the kernel.
> O(128) is still O(1) for instance. Having to search a bit in a PAGE is
> a sensible compromise, if we dont add overhead on each fget() calls.
hm, i'm not sure what you are talking about here. Look at Davide's stuff
- it's clearly not O(128)...
> You add conditional branches on very hot spots.
>
> When you open/close a file, you need to access previous and next
> cells, so you need 3 cache lines, exactly like current *legacy* code.
> (one for file pointer, one on each bitmap flags(open/close_on_exec) )
the fd spaces will be separated _no matter what_, that is a physical
inevitability of the ABI in question. Whether you hide that into 'extra
complexity by trying to bend bitmaps in a way that the new users dont
need' or do it explicitly like Davide, i'll go for the explicit
separation. Davide's approach, besides being cleaner, simpler and faster
also has the advantage of enabling the possible demoting of the 'legacy'
fd space in the future. Or demoting the 'new' fd space in the future, if
the interface does not take off.
Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
