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Re: [Qemu-devel] [PATCH 13/16] translate-all: protect TB jumps with a pe
From: |
Laurent Desnogues |
Subject: |
Re: [Qemu-devel] [PATCH 13/16] translate-all: protect TB jumps with a per-destination-TB lock |
Date: |
Tue, 27 Feb 2018 12:43:59 +0100 |
On Tue, Feb 27, 2018 at 12:33 PM, Paolo Bonzini <address@hidden> wrote:
> On 27/02/2018 06:39, Emilio G. Cota wrote:
>> Using a hash table or a binary tree to keep track of the jumps
>> doesn't really pay off, not only due to the increased memory usage,
>> but also because most TBs have only 0 or 1 jumps to them. The maximum
>> number of jumps when booting debian-arm that I measured is 35, but
>> as we can see in the histogram below a TB with that many incoming jumps
>> is extremely rare; the average TB has 0.80 incoming jumps.
>>
>> n_jumps: 379208; avg jumps/tb: 0.801099
>> dist: [0.0,1.0)|▄█▁▁▁▁▁▁▁▁▁▁▁ ▁▁▁▁▁▁ ▁▁▁ ▁▁▁ ▁|[34.0,35.0]
>
> This makes sense, for example:
>
> while(...) {
> }
>
> 2 basic blocks, 0 and 1 incoming jumps (avg 0.5)
>
> if(...) {
> }
>
> 2 basic blocks, 0 and 1 incoming jumps (avg 0.5)
>
> if(...) {
> } else {
> }
>
> 3 basic blocks, 0, 1 and 1 incoming jumps (avg 0.66)
>
> So 0.8 is actually a lot. :) The long tail is probably for switch
> statements.
And calls too :-)
Laurent
> Paolo
>
- [Qemu-devel] [PATCH 00/16] tcg: tb_lock removal redux v1, Emilio G. Cota, 2018/02/27
- [Qemu-devel] [PATCH 07/16] translate-all: remove hole in PageDesc, Emilio G. Cota, 2018/02/27
- [Qemu-devel] [PATCH 06/16] translate-all: make l1_map lockless, Emilio G. Cota, 2018/02/27
- [Qemu-devel] [PATCH 09/16] translate-all: move tb_invalidate_phys_page_range up in the file, Emilio G. Cota, 2018/02/27
- [Qemu-devel] [PATCH 12/16] translate-all: discard TB when tb_link_page returns an existing matching TB, Emilio G. Cota, 2018/02/27
- [Qemu-devel] [PATCH 01/16] qht: require a default comparison function, Emilio G. Cota, 2018/02/27