Messages in this thread | | | Subject | Re: [PATCH v4 08/21] x86/resctrl: Switch over to the resctrl mbps_val list | From | James Morse <> | Date | Tue, 7 Jun 2022 13:07:24 +0100 |
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Hi Reinette,
On 17/05/2022 17:19, Reinette Chatre wrote: > On 4/12/2022 5:44 AM, James Morse wrote: >> Updates to resctrl's software controller follow the same path as >> other configuration updates, but they don't modify the hardware state. >> rdtgroup_schemata_write() uses parse_line() and the resource's >> parse_ctrlval() function to stage the configuration. >> resctrl_arch_update_domains() then updates the mbps_val[] array >> instead, and resctrl_arch_update_domains() skips the rdt_ctrl_update() >> call that would update hardware. >> >> This complicates the interface between resctrl's filesystem parts >> and architecture specific code. It should be possible for mba_sc >> to be completely implemented by the filesystem parts of resctrl. This >> would allow it to work on a second architecture with no additional code. >> resctrl_arch_update_domains() using the mbps_val[] array prevents this. >> >> Change parse_bw() to write the configuration value directly to the >> mbps_val[] array in the domain structure. Change rdtgroup_schemata_write() >> to skip the call to resctrl_arch_update_domains(), meaning all the >> mba_sc specific code in resctrl_arch_update_domains() can be removed. >> On the read-side, show_doms() and update_mba_bw() are changed to read >> the mbps_val[] array from the domain structure. With this, >> resctrl_arch_get_config() no longer needs to consider mba_sc resources.
> This sounds like a good cleanup and I understand it to not intend > functional change, so a bit more information is needed on the change > in rdtgroup_init_alloc(). More below.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index 9d5be6a73644..07904308245c 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> @@ -1932,11 +1937,6 @@ static int set_mba_sc(bool mba_sc) >> >> r->membw.mba_sc = mba_sc; >> >> - list_for_each_entry(d, &r->domains, list) { >> - for (i = 0; i < num_closid; i++) >> - d->mbps_val[i] = MBA_MAX_MBPS; >> - } >> - >> return 0; >> }
> With this removed, where is rdt_domain->mbps_val reset on remount of resctrl?
Oops, this is a bug. Its a left over from when the rdt_domain->mbps_val[] array was only allocated when mba_sc was enabled.
>> @@ -2809,15 +2809,18 @@ static int rdtgroup_init_cat(struct resctrl_schema *s, u32 closid) >> } >> >> /* Initialize MBA resource with default values. */ >> -static void rdtgroup_init_mba(struct rdt_resource *r) >> +static void rdtgroup_init_mba(struct rdt_resource *r, u32 closid) >> { >> struct resctrl_staged_config *cfg; >> struct rdt_domain *d; >> >> list_for_each_entry(d, &r->domains, list) { >> cfg = &d->staged_config[CDP_NONE]; >> - cfg->new_ctrl = is_mba_sc(r) ? MBA_MAX_MBPS : r->default_ctrl; >> + cfg->new_ctrl = r->default_ctrl; >> cfg->have_new_ctrl = true; >> + >> + if (is_mba_sc(r)) >> + d->mbps_val[closid] = MBA_MAX_MBPS; >> } >> } >> >> @@ -2831,7 +2834,7 @@ static int rdtgroup_init_alloc(struct rdtgroup *rdtgrp) >> list_for_each_entry(s, &resctrl_schema_all, list) { >> r = s->res; >> if (r->rid == RDT_RESOURCE_MBA) { >> - rdtgroup_init_mba(r); >> + rdtgroup_init_mba(r, rdtgrp->closid); >> } else { >> ret = rdtgroup_init_cat(s, rdtgrp->closid); >> if (ret < 0) > > What follows this hunk and continues to be called is: > > ret = resctrl_arch_update_domains(r, rdtgrp->closid); > > before this patch resctrl_arch_update_domains() would just have updated > the mbps_val but not made any configuration changed if is_mba_sc() is true. > Before this patch configuration changes done in > resctrl_arch_update_domains() is omitted when is_mba_sc() is true > but after earlier change in this patch it proceeds and will result in > configuration change.
Yes, this will write the default ctrl_val into hardware. Previously it may have an unknown value from a previous allocation of the closid, update_mba_bw() will eventually adjust that to something sensible.
I think I ignored this as harmless, but I agree its better to keep the existing behaviour. I'll add: | if (is_mba_sc(r)) | continue;
to both rdtgroup_init_mba() and rdtgroup_init_alloc().
Thanks,
James
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