Re: [Qemu-devel] [RFC PATCH] qht: Align sequence lock to cache line

[Paolo Bonzini]

On 25/10/2016 17:49, Pranith Kumar wrote:
> But we are taking the seqlock of only the head bucket, while the
> readers are reading hashes/pointers of the chained buckets.

No, we aren't.  See qht_lookup__slowpath.

This patch:

throughput base   patch  %change
update
0          8.07   13.33  +65%
10         7.10   8.90   +25%
20         6.34   7.02   +10%
30         5.48   6.11   +9.6%
40         4.90   5.46   +11.42%


Just doubling the cachesize:

throughput base   patch  %change
update
0          8.07   4.47   -45% ?!?
10         7.10   9.82   +38%
20         6.34   8.13   +28%
30         5.48   7.13   +30%
40         5.90   6.45   +30%

It seems to me that your machine has 128-byte cachelines.

Paolo