On 20/04/2020 15:12, Jan Beulich wrote: > On 17.04.2020 17:50, Andrew Cooper wrote: >> There is no need for the Compat GDT if there are no 32bit PV guests. This >> saves 4k per online CPU >> >> Bloat-o-meter reports the following savings in Xen itself: >> >> add/remove: 0/3 grow/shrink: 1/4 up/down: 7/-4612 (-4605) >> Function old new delta >> cpu_smpboot_free 1249 1256 +7 >> per_cpu__compat_gdt_l1e 8 - -8 >> per_cpu__compat_gdt 8 - -8 >> init_idt_traps 442 420 -22 >> load_system_tables 414 364 -50 >> trap_init 444 280 -164 >> cpu_smpboot_callback 1255 991 -264 >> boot_compat_gdt 4096 - -4096 >> Total: Before=3062726, After=3058121, chg -0.15% >> >> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> >> --- >> CC: Jan Beulich <jbeul...@suse.com> >> CC: Wei Liu <w...@xen.org> >> CC: Roger Pau Monné <roger....@citrix.com> >> >> The increase in cpu_smpboot_free() appears to be a consequence of a totally >> different layout of basic blocks. >> --- >> xen/arch/x86/cpu/common.c | 5 +++-- >> xen/arch/x86/desc.c | 2 ++ >> xen/arch/x86/smpboot.c | 5 ++++- >> xen/arch/x86/traps.c | 10 +++++++--- >> 4 files changed, 16 insertions(+), 6 deletions(-) >> >> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c >> index 1b33f1ed71..7b093cb421 100644 >> --- a/xen/arch/x86/cpu/common.c >> +++ b/xen/arch/x86/cpu/common.c >> @@ -752,8 +752,9 @@ void load_system_tables(void) >> >> _set_tssldt_desc(gdt + TSS_ENTRY, (unsigned long)tss, >> sizeof(*tss) - 1, SYS_DESC_tss_avail); >> - _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss, >> - sizeof(*tss) - 1, SYS_DESC_tss_busy); >> + if ( IS_ENABLED(CONFIG_PV32) ) >> + _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss, >> + sizeof(*tss) - 1, SYS_DESC_tss_busy); > Wouldn't this better be "if ( opt_pv32 )"? Also elsewhere then.
Doing it like this specifically ensures that there is never a case where things are half configured. I don't think it is wise to suggest that making opt_pv32 runtime configurable might work. ~Andrew
