AuxXxilium/linux_dsm_epyc7002
1
0
Fork 0
mirror of https://github.com/AuxXxilium/linux_dsm_epyc7002.git synced 2024-12-14 16:36:55 +07:00
Code Issues Actions Packages Projects Releases Wiki Activity

x86-32: make sure clts is batched during context switch

Browse Source 
If we're preloading the fpu state during context switch, make sure the clts
happens while we're batching the cpu context update, then do the actual
__math_state_restore once the updates are flushed.

This allows more efficient context switches when running paravirtualized,
as all the hypercalls can be folded together into one.

[ Impact: optimise paravirtual FPU context switch ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Alok Kataria <akataria@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Jeremy Fitzhardinge 2009-04-24 00:45:26 -07:00
parent e6e9cac8c3
commit 2fcddce10f
1 changed files with 16 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
arch/x86/kernel/process_32.c
View File

@ -350,14 +350,21 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
*next = &next_p->thread; *next = &next_p->thread;
int cpu = smp_processor_id(); int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu); struct tss_struct *tss = &per_cpu(init_tss, cpu);
bool preload_fpu;
/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */ /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
/*
* If the task has used fpu the last 5 timeslices, just do a full
* restore of the math state immediately to avoid the trap; the
* chances of needing FPU soon are obviously high now
*/
preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5;
__unlazy_fpu(prev_p); __unlazy_fpu(prev_p);
/* we're going to use this soon, after a few expensive things */ /* we're going to use this soon, after a few expensive things */
if (next_p->fpu_counter > 5) if (preload_fpu)
prefetch(next->xstate); prefetch(next->xstate);
/* /*
@ -398,6 +405,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT)) task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
__switch_to_xtra(prev_p, next_p, tss); __switch_to_xtra(prev_p, next_p, tss);
/* If we're going to preload the fpu context, make sure clts
is run while we're batching the cpu state updates. */
if (preload_fpu)
clts();
/* /*
* Leave lazy mode, flushing any hypercalls made here. * Leave lazy mode, flushing any hypercalls made here.
* This must be done before restoring TLS segments so * This must be done before restoring TLS segments so
@ -407,15 +419,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
*/ */
arch_end_context_switch(next_p); arch_end_context_switch(next_p);
/* If the task has used fpu the last 5 timeslices, just do a full if (preload_fpu)
* restore of the math state immediately to avoid the trap; the __math_state_restore();
* chances of needing FPU soon are obviously high now
*
* tsk_used_math() checks prevent calling math_state_restore(),
* which can sleep in the case of !tsk_used_math()
*/
if (tsk_used_math(next_p) && next_p->fpu_counter > 5)
math_state_restore();
/* /*
* Restore %gs if needed (which is common) * Restore %gs if needed (which is common)