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By directly caching data from I/O > devices rather than first storing the I/O data in DRAM, feature reduces > the demands on DRAM bandwidth and reduces latency to the processor > consuming the I/O data. This provides good context but the changelog does not mention what this patch does. An idea to get started (please improve): Data from I/O devices can be inserted directly into L3 cache. This reduces demands on DRAM bandwidth and reduces latency to the processor consuming the I/O data. Introduce cache resource property "io_alloc_capable" that an architecture can set if a portion of the L3 cache can be allocated for I/O traffic. Set this property on x86 systems that support SDCIAE. > > Signed-off-by: Babu Moger > --- > v3: Rewrote commit log. Changed the text to bit generic than the AMD specific. > Renamed the rdt_get_sdciae_alloc_cfg() to rdt_set_io_alloc_capable(). > Removed leftover comment from v2. > > v2: Changed sdciae_capable to io_alloc_capable to make it generic feature. > Also moved the io_alloc_capable in struct resctrl_cache. > --- > arch/x86/kernel/cpu/resctrl/core.c | 7 +++++++ > include/linux/resctrl.h | 3 +++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c > index c2450cd52511..1ebdb2dcc009 100644 > --- a/arch/x86/kernel/cpu/resctrl/core.c > +++ b/arch/x86/kernel/cpu/resctrl/core.c > @@ -306,6 +306,11 @@ static void rdt_get_cdp_config(int level) > rdt_resources_all[level].r_resctrl.cdp_capable = true; > } > > +static void rdt_set_io_alloc_capable(struct rdt_resource *r) > +{ > + r->cache.io_alloc_capable = true; > +} > + > static void rdt_get_cdp_l3_config(void) > { > rdt_get_cdp_config(RDT_RESOURCE_L3); > @@ -931,6 +936,8 @@ static __init bool get_rdt_alloc_resources(void) > rdt_get_cache_alloc_cfg(1, r); > if (rdt_cpu_has(X86_FEATURE_CDP_L3)) > rdt_get_cdp_l3_config(); > + if (rdt_cpu_has(X86_FEATURE_SDCIAE)) > + rdt_set_io_alloc_capable(r); > ret = true; > } > if (rdt_cpu_has(X86_FEATURE_CAT_L2)) { > diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h > index d94abba1c716..dbe6461f3fbc 100644 > --- a/include/linux/resctrl.h > +++ b/include/linux/resctrl.h > @@ -129,6 +129,8 @@ struct rdt_mon_domain { > * @arch_has_sparse_bitmasks: True if a bitmask like f00f is valid. > * @arch_has_per_cpu_cfg: True if QOS_CFG register for this cache > * level has CPU scope. > + * @io_alloc_capable: True if portion of the L3 cache can be allocated > + * for I/O traffic. Enforcing that this should be for L3 cache is confusing. On a system with L3 and L2 cache resources each resource will be described by the properties in struct resctrl_cache for particular resource. We do not want to set "io_alloc_capable" to true in the L2's struct if the L3 cache supports this feature. This can just be: "True if portion of the cache can be allocated for I/O traffic" > */ > struct resctrl_cache { > unsigned int cbm_len; > @@ -136,6 +138,7 @@ struct resctrl_cache { > unsigned int shareable_bits; > bool arch_has_sparse_bitmasks; > bool arch_has_per_cpu_cfg; > + bool io_alloc_capable; > }; > > /** Reinette