On Thu, 2018-03-15 at 18:30 -0700, Matthew Wilcox wrote: > On Thu, Mar 15, 2018 at 11:58:07PM +0000, Saeed Mahameed wrote: > > On Wed, 2018-03-14 at 19:57 -0700, Matthew Wilcox wrote: > > > From: Matthew Wilcox <mawil...@microsoft.com> > > > > > > The mlx5 driver calls ida_pre_get() in a loop for no readily > > > apparent > > > reason. The driver uses ida_simple_get() which will call > > > ida_pre_get() > > > by itself and there's no need to use ida_pre_get() unless using > > > ida_get_new(). > > > > > > > Hi Matthew, > > > > Is this is causing any issues ? or just a simple cleanup ? > > I'm removing the API. At the end of this cleanup, there will be no > more > preallocation; instead we will rely on the slab allocator not > sucking. >
Ok, Seems reasonable, I am ok with this. > > Adding Maor, the author of this change, > > > > I believe the idea is to speed up insert_fte (which calls > > ida_simple_get) since insert_fte runs under the FTE write > > semaphore, > > in this case if ida_pre_get was successful before taking the > > semaphore > > for all the FTE nodes in the loop, this will be a huge win for > > ida_simple_get which will immediately return success without even > > trying to allocate. > > I think that's misguided. The IDA allocator is only going to > allocate > memory once in every 1024 allocations. Also, it does try to > allocate, > even if there are preallocated nodes. So you're just wasting time, > unfortunately. > Well just by looking at the code you can tell for sure that two consecutive calls to ida_pre_get will result in one allocation only. due to "if (!this_cpu_read(ida_bitmap))" but i didn't dig into details and didn't go through the whole ida_get_new_above, so i will count on your judgment here. Still i would like to wait for Maor's input here, the author.. I Will ping him today. Thanks, Saeed.
