On 29/10/25 11:31, Frederic Weisbecker wrote: > Le Wed, Oct 29, 2025 at 11:16:23AM +0100, Valentin Schneider a écrit : >> On 28/10/25 16:59, Frederic Weisbecker wrote: >> > Le Fri, Oct 10, 2025 at 05:38:37PM +0200, Valentin Schneider a écrit : >> >> @@ -171,8 +172,27 @@ For 32-bit we have the following conventions - >> >> kernel is built with >> >> andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg >> >> .endm >> >> >> >> -.macro COALESCE_TLBI >> >> +.macro COALESCE_TLBI scratch_reg:req >> >> #ifdef CONFIG_COALESCE_TLBI >> >> + /* No point in doing this for housekeeping CPUs */ >> >> + movslq PER_CPU_VAR(cpu_number), \scratch_reg >> >> + bt \scratch_reg, tick_nohz_full_mask(%rip) >> >> + jnc .Lend_tlbi_\@ >> > >> > I assume it's not possible to have a static call/branch to >> > take care of all this ? >> > >> >> I think technically yes, but that would have to be a per-cpu patchable >> location, which would mean something like each CPU having its own copy of >> that text page... Unless there's some existing way to statically optimize >> >> if (cpumask_test_cpu(smp_processor_id(), mask)) >> >> where @mask is a boot-time constant (i.e. the nohz_full mask). > > Or just check housekeeping_overriden static key before everything. This one is > enabled only if either nohz_full, isolcpus or cpuset isolated partition (well, > it's on the way for the last one) are running, but those are all niche, which > means you spare 99.999% kernel usecases. >
Oh right, if NOHZ_FULL is actually in use. Yeah that housekeeping key could do since, at least for the cmdline approach, it's set during start_kernel(). I need to have a think about the runtime cpuset case. Given we have ALTERNATIVE's in there I assume something like a boot-time-driven static key could do, but I haven't found out yet if and how that can be shoved in an ASM file. > Thanks. > >> >> > Thanks. >> > >> > -- >> > Frederic Weisbecker >> > SUSE Labs >> >> > > -- > Frederic Weisbecker > SUSE Labs
