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| author |   Cosmin Ratiu <cratiu@nvidia.com> | 2024-10-01 13:37:07 +0300 |
|---|---|---|
| committer |   Jakub Kicinski <kuba@kernel.org> | 2024-10-04 11:33:46 -0700 |
| commit | d95f77f1196a9458f61a08faa0eb569cf6f03a84 (patch) | |
| tree | 13d1c28b0727ae7e1156b50d2a6f1f89b91b97ed | |
| parent | net/mlx5: hw counters: Replace IDR+lists with xarray (diff) | |
| download | linux-rng-d95f77f1196a9458f61a08faa0eb569cf6f03a84.tar.xz linux-rng-d95f77f1196a9458f61a08faa0eb569cf6f03a84.zip | |
net/mlx5: hw counters: Drop unneeded cacheline alignment
The mlx5_fc struct has a cache for values queried from hw, which is
cacheline aligned. On x86_64, this results in:
struct mlx5_fc {
u32 id; /* 0 4 */
bool aging; /* 4 1 */
/* XXX 3 bytes hole, try to pack */
struct mlx5_fc_bulk * bulk; /* 8 8 */
/* XXX 48 bytes hole, try to pack */
/* --- cacheline 1 boundary (64 bytes) --- */
struct mlx5_fc_cache cache __attribute__((__aligned__(64)));
/* 64 24 */
u64 lastpackets; /* 88 8 */
u64 lastbytes; /* 96 8 */
/* size: 128, cachelines: 2, members: 6 */
/* sum members: 53, holes: 2, sum holes: 51 */
/* padding: 24 */
/* forced aligns: 1, forced holes: 1, sum forced holes: 48 */
} __attribute__((__aligned__(64)));
(output from pahole).
...So a 48+24=72 byte waste. As far as I can determine, this serves no
purpose other than maybe making sure that the values in the cache do not
span two cachelines in the worst case scenario, but that's not a valid
enough reason to waste 72 bytes per counter, especially since this code
is not performance-critical. There could potentially be hundreds of
thousands of counters (e.g. for connection-tracking), so this quickly
adds up to multiple MB wasted.
This commit removes the alignment, resulting in:
struct mlx5_fc {
[...]
/* size: 56, cachelines: 1, members: 6 */
/* sum members: 53, holes: 1, sum holes: 3 */
/* last cacheline: 56 bytes */
};
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20241001103709.58127-5-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
| -rw-r--r-- | drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c b/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c index 05d9351ff577..ef13941e55c2 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c @@ -53,7 +53,7 @@ struct mlx5_fc { u32 id; bool aging; struct mlx5_fc_bulk *bulk; - struct mlx5_fc_cache cache ____cacheline_aligned_in_smp; + struct mlx5_fc_cache cache; /* last{packets,bytes} are used for calculating deltas since last reading. */ u64 lastpackets; u64 lastbytes; |