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Subject[PATCH v2] x86/timers: Move simple_udelay_calibration() past kvmclock_init()
Date
simple_udelay_calibration() relies on x86_platform's calibration ops.
For KVM these ops are set late in setup_arch() and so
simple_udelay_calibration() ends up using native version.

Besides being possibly incorrect, this significantly increases kernel
boot time. For example, on my laptop executing start_kernel() by a guest
takes ~10 times more than when KVM's ops are used.

Since early_xdbc_setup_hardware() relies on calibration having been
performed move it too.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
v2:
* Move xdbc initialization down as well.

Alternatively, we could start calling simple_udelay_calibration() only
on bare metal: My understanding is that the only reason it exists is to
help with USB3 earlyprink driver, which I don't think is useful to guests
anyway.

arch/x86/kernel/setup.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f81823695014..6e0e747d53bf 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1039,8 +1039,6 @@ void __init setup_arch(char **cmdline_p)
*/
init_hypervisor_platform();

- simple_udelay_calibration();
-
x86_init.resources.probe_roms();

/* after parse_early_param, so could debug it */
@@ -1118,9 +1116,6 @@ void __init setup_arch(char **cmdline_p)
memblock_set_current_limit(ISA_END_ADDRESS);
e820__memblock_setup();

- if (!early_xdbc_setup_hardware())
- early_xdbc_register_console();
-
reserve_bios_regions();

if (efi_enabled(EFI_MEMMAP)) {
@@ -1221,6 +1216,10 @@ void __init setup_arch(char **cmdline_p)
kvmclock_init();
#endif

+ simple_udelay_calibration();
+ if (!early_xdbc_setup_hardware())
+ early_xdbc_register_console();
+
x86_init.paging.pagetable_init();

kasan_init();
--
2.11.0
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