Messages in this thread Patch in this message | | | Date | Tue, 7 Jun 2022 15:08:16 -0700 | From | Fenghua Yu <> | Subject | Re: [PATCH v4 19/21] x86/resctrl: Rename and change the units of resctrl_cqm_threshold |
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Hi, James,
On Tue, Apr 12, 2022 at 12:44:17PM +0000, James Morse wrote: > resctrl_cqm_threshold is stored in a hardware specific chunk size, > but exposed to user-space as bytes. > > This means the filesystem parts of resctrl need to know how the hardware > counts, to convert the user provided byte value to chunks. The interface > between the architecture's resctrl code and the filesystem ought to > treat everything as bytes. > > Change the unit of resctrl_cqm_threshold to bytes. resctrl_arch_rmid_read() > still returns its value in chunks, so this needs converting to bytes. > As all the users have been touched, rename the variable to > resctrl_rmid_realloc_threshold, which describes what the value is for. > > Neither r->num_rmid nor hw_res->mon_scale are guaranteed to be a power > of 2, so the existing code introduces a rounding error from resctrl's > theoretical fraction of the cache usage. This behaviour is kept as it > ensures the user visible value matches the value read from hardware > when the rmid will be reallocated. > > Reviewed-by: Jamie Iles <quic_jiles@quicinc.com> > Tested-by: Xin Hao <xhao@linux.alibaba.com> > Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com> > Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com> > Tested-by: Cristian Marussi <cristian.marussi@arm.com> > Signed-off-by: James Morse <james.morse@arm.com> > --- > Changes since v3: > * Preserved the rounding errors. > --- > arch/x86/kernel/cpu/resctrl/internal.h | 1 - > arch/x86/kernel/cpu/resctrl/monitor.c | 41 +++++++++++++++----------- > arch/x86/kernel/cpu/resctrl/rdtgroup.c | 9 ++---- > include/linux/resctrl.h | 2 ++ > 4 files changed, 28 insertions(+), 25 deletions(-) > > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h > index bdb55c2fbdd3..c05e9b7cf77a 100644 > --- a/arch/x86/kernel/cpu/resctrl/internal.h > +++ b/arch/x86/kernel/cpu/resctrl/internal.h > @@ -98,7 +98,6 @@ struct rmid_read { > u64 val; > }; > > -extern unsigned int resctrl_cqm_threshold; > extern bool rdt_alloc_capable; > extern bool rdt_mon_capable; > extern unsigned int rdt_mon_features; > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c > index 88988de0c96c..00f6e27e4e0d 100644 > --- a/arch/x86/kernel/cpu/resctrl/monitor.c > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c > @@ -37,8 +37,8 @@ static LIST_HEAD(rmid_free_lru); > * @rmid_limbo_count count of currently unused but (potentially) > * dirty RMIDs. > * This counts RMIDs that no one is currently using but that > - * may have a occupancy value > intel_cqm_threshold. User can change > - * the threshold occupancy value. > + * may have a occupancy value > resctrl_rmid_realloc_threshold. User can > + * change the threshold occupancy value. > */ > static unsigned int rmid_limbo_count; > > @@ -59,10 +59,10 @@ bool rdt_mon_capable; > unsigned int rdt_mon_features; > > /* > - * This is the threshold cache occupancy at which we will consider an > + * This is the threshold cache occupancy in bytes at which we will consider an > * RMID available for re-allocation. > */ > -unsigned int resctrl_cqm_threshold; > +unsigned int resctrl_rmid_realloc_threshold; > > #define CF(cf) ((unsigned long)(1048576 * (cf) + 0.5)) > > @@ -223,14 +223,13 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d, > */ > void __check_limbo(struct rdt_domain *d, bool force_free) > { > + struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > + struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); > struct rmid_entry *entry; > - struct rdt_resource *r; > u32 crmid = 1, nrmid; > bool rmid_dirty; > u64 val = 0; > > - r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > - > /* > * Skip RMID 0 and start from RMID 1 and check all the RMIDs that > * are marked as busy for occupancy < threshold. If the occupancy > @@ -245,10 +244,12 @@ void __check_limbo(struct rdt_domain *d, bool force_free) > entry = __rmid_entry(nrmid); > > if (resctrl_arch_rmid_read(r, d, entry->rmid, > - QOS_L3_OCCUP_EVENT_ID, &val)) > + QOS_L3_OCCUP_EVENT_ID, &val)) { > rmid_dirty = true; > - else > - rmid_dirty = (val >= resctrl_cqm_threshold); > + } else { > + val *= hw_res->mon_scale; > + rmid_dirty = (val >= resctrl_rmid_realloc_threshold); > + } > > if (force_free || !rmid_dirty) { > clear_bit(entry->rmid, d->rmid_busy_llc); > @@ -289,13 +290,12 @@ int alloc_rmid(void) > > static void add_rmid_to_limbo(struct rmid_entry *entry) > { > - struct rdt_resource *r; > + struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > + struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); > struct rdt_domain *d; > int cpu, err; > u64 val = 0; > > - r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > - > entry->busy = 0; > cpu = get_cpu(); > list_for_each_entry(d, &r->domains, list) { > @@ -303,7 +303,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry) > err = resctrl_arch_rmid_read(r, d, entry->rmid, > QOS_L3_OCCUP_EVENT_ID, > &val); > - if (err || val <= resctrl_cqm_threshold) > + val *= hw_res->mon_scale; > + if (err || val <= resctrl_rmid_realloc_threshold) > continue; > } > > @@ -744,6 +745,7 @@ int rdt_get_mon_l3_config(struct rdt_resource *r) > unsigned int mbm_offset = boot_cpu_data.x86_cache_mbm_width_offset; > struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); > unsigned int cl_size = boot_cpu_data.x86_cache_size; > + unsigned int threshold; > int ret; > > hw_res->mon_scale = boot_cpu_data.x86_cache_occ_scale; > @@ -762,10 +764,15 @@ int rdt_get_mon_l3_config(struct rdt_resource *r) > * > * For a 35MB LLC and 56 RMIDs, this is ~1.8% of the LLC. > */ > - resctrl_cqm_threshold = cl_size * 1024 / r->num_rmid; > + threshold = cl_size * 1024 / r->num_rmid; > > - /* h/w works in units of "boot_cpu_data.x86_cache_occ_scale" */
Could you please keep this comment? This comment is still helpful and meaningful in the context.
> - resctrl_cqm_threshold /= hw_res->mon_scale; > + /* > + * Because num_rmid may not be a power of two, round the value > + * to the nearest multiple of hw_res->mon_scale so it matches a > + * value the hardware will measure. mon_scale may not be a power of 2. > + */ > + threshold /= hw_res->mon_scale; > + resctrl_rmid_realloc_threshold = threshold * hw_res->mon_scale; > > ret = dom_data_init(r); > if (ret) > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > index f494ca6b8bdd..7c35561e5216 100644 > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > @@ -1030,10 +1030,7 @@ static int rdt_delay_linear_show(struct kernfs_open_file *of, > static int max_threshold_occ_show(struct kernfs_open_file *of, > struct seq_file *seq, void *v) > { > - struct rdt_resource *r = of->kn->parent->priv; > - struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); > - > - seq_printf(seq, "%u\n", resctrl_cqm_threshold * hw_res->mon_scale); > + seq_printf(seq, "%u\n", resctrl_rmid_realloc_threshold); > > return 0; > } > @@ -1055,7 +1052,6 @@ static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of, > static ssize_t max_threshold_occ_write(struct kernfs_open_file *of, > char *buf, size_t nbytes, loff_t off) > { > - struct rdt_hw_resource *hw_res; > unsigned int bytes; > int ret; > > @@ -1066,8 +1062,7 @@ static ssize_t max_threshold_occ_write(struct kernfs_open_file *of, > if (bytes > (boot_cpu_data.x86_cache_size * 1024)) > return -EINVAL; > > - hw_res = resctrl_to_arch_res(of->kn->parent->priv); > - resctrl_cqm_threshold = bytes / hw_res->mon_scale; > + resctrl_rmid_realloc_threshold = bytes;
Shouldn't bytes be multiples of hw_res->mon_scale? If user inputs non-multiples value, resctrl_rmid_realloc_threshold will keep the value in the kernel. Is that right?
But if you convert the input into multiples, user may see a different value when read it.
Does this argument override the reason why this patch is needed?
> > return nbytes; > } > diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h > index cc6311a40582..fc4805901f1a 100644 > --- a/include/linux/resctrl.h > +++ b/include/linux/resctrl.h > @@ -250,4 +250,6 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d, > void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d, > u32 rmid, enum resctrl_event_id eventid); > > +extern unsigned int resctrl_rmid_realloc_threshold; > + > #endif /* _RESCTRL_H */ > -- > 2.30.2 >
Thanks.
-Fenghua
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