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| author | chenhuguanshen <chenhgs@chinatelecom.cn> | 2026-08-12 15:04:59 +0800 |
|---|---|---|
| committer | Marek Szyprowski <m.szyprowski@samsung.com> | 2026-08-13 08:02:35 +0200 |
| commit | 121f9fd1c3083312055126205f3e40b8ee999fe6 (patch) | |
| tree | c6eaf65fb285e65972a61c4e0a0d994773cbd08e /include/linux | |
| parent | 298d312c0ff3f49061316ba799257277f4bb9bc4 (diff) | |
| download | linux-next-121f9fd1c3083312055126205f3e40b8ee999fe6.tar.gz linux-next-121f9fd1c3083312055126205f3e40b8ee999fe6.zip | |
dma/swiotlb: decouple high watermark tracking from CONFIG_DEBUG_FS
Under heavy concurrent DMA traffic on CoCo VMs, inc_used_and_hiwater()
performs an atomic_long_add_return() plus a CAS loop on the global
used_hiwater, and dec_used() performs an atomic_long_sub() on total_used.
All CPUs contend on the same cacheline, causing measurable throughput
degradation at scale.
Historically these counters were only compiled in under CONFIG_DEBUG_FS,
which means production kernels with debugfs paid the atomic overhead
unconditionally. Make the tracking boot-time opt-in instead so that it
is disabled by default with near-zero overhead via static_call, and can
be enabled via "swiotlb=track_hiwater" parameter on demand for debugging.
Note that when CONFIG_DEBUG_FS is enabled but hiwater tracking is disabled,
the "io_tlb_used" metric reports an approximate value rather than an
instantaneously exact one.
Suggested-by: Fan Du <fan.du@intel.com>
Signed-off-by: Jun Miao <jun.miao@intel.com>
Co-developed-by: Fan Du <fan.du@intel.com>
Signed-off-by: Fan Du <fan.du@intel.com>
Tested-by: chenhuguanshen <chenhgs@chinatelecom.cn>
Signed-off-by: chenhuguanshen <chenhgs@chinatelecom.cn>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20260812070459.637077-1-frankchen158@126.com
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/swiotlb.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index 1665a9ce8f94..318bb1beb07f 100644 --- a/include/linux/swiotlb.h +++ b/include/linux/swiotlb.h @@ -102,10 +102,10 @@ struct io_tlb_pool { * @pools: List of IO TLB memory pool descriptors (if dynamic). * @dyn_alloc: Dynamic IO TLB pool allocation work. * @total_used: The total number of slots in the pool that are currently used - * across all areas. Used only for calculating used_hiwater in - * debugfs. - * @used_hiwater: The high water mark for total_used. Used only for reporting - * in debugfs. + * across all areas. Used only for calculating used_hiwater via boot + * parameter swiotlb=track_hiwater and exposed via debugfs. + * @used_hiwater: The high water mark for total_used. Can be enabled at boot + * time via swiotlb=track_hiwater and exposed via debugfs. * @transient_nslabs: The total number of slots in all transient pools that * are currently used across all areas. */ |