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 <mawilcox@xxxxxxxxxxxxx>
> > >
> > > 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,
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