Messages in this thread | | | From | Don Mullis <> | Subject | Re: [PATCH 1/2] lib: more scalable list_sort() | Date | Fri, 22 Jan 2010 09:55:39 -0800 |
| |
Artem Bityutskiy <dedekind@infradead.org> writes:
> On Fri, 2010-01-22 at 11:43 +0100, Andi Kleen wrote: >> Don Mullis <don.mullis@gmail.com> writes: >> > >> > Being just a dumb library routine, list_sort() has no idea what context >> > it's been called in, how long a list a particular client could pass in, >> > nor how expensive the client's cmp() callback might be. >> > >> > The cmp() callback already passes back a client-private pointer. >> > Hanging off of this could be a count of calls, or timing information, >> > maintained by the client. Whenever some threshold is reached, the >> > client's cmp() could do whatever good CPU-sharing citizenship required. >> >> need_resched() does all the timing/thresholding (it checks the >> reschedule flag set by the timer interrupt). You just have to call it. >> But preferable not in the inner loop, but in a outer one. It's >> not hyper-expensive, but it's not free either. >> >> The drawback is that if it's called the context always has to >> allow sleeping, so it might need to be optional. >> >> Anyways a better fix might be simply to ensure in the caller >> that lists never get as long that they become a scheduling >> hazard. But you indicated that ubifs would pass very long lists? >> Perhaps ubifs (and other calls who might have that problem) simply >> needs to be fixed. > > No, they are not very long. A hundred or so I guess, rarely. But we need > to check what is really the worst case, but it should not be too many.
I suggest for now we leave scheduling issues as the caller's responsibility, and keep list_sort() simple. Wouldn't want to be getting any email like this:
http://lwn.net/Articles/366768/
| |