lkml.org 
[lkml]   [2022]   [Jan]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch v8 03/10] task isolation: sync vmstats on return to userspace
On Thu, Jan 27, 2022 at 01:47:07PM -0300, Marcelo Tosatti wrote:
> > > @@ -177,6 +179,9 @@ static unsigned long exit_to_user_mode_l
> > > /* Architecture specific TIF work */
> > > arch_exit_to_user_mode_work(regs, ti_work);
> > >
> > > + if (tsk_isol_work)
> > > + isolation_exit_to_user_mode();
> > > +
> > > /*
> > > * Disable interrupts and reevaluate the work flags as they
> > > * might have changed while interrupts and preemption was
> > > @@ -188,6 +193,7 @@ static unsigned long exit_to_user_mode_l
> > > tick_nohz_user_enter_prepare();
> > >
> > > ti_work = READ_ONCE(current_thread_info()->flags);
> > > + tsk_isol_work = task_isol_has_work();
> >
> > Shouldn't it be a TIF_FLAG part of EXIT_TO_USER_MODE_WORK instead?
> >
> > Thanks.
>
> static inline int task_isol_has_work(void)
> {
> int cpu, ret;
> struct isol_info *i;
>
> if (likely(current->task_isol_info == NULL))
> return 0;
>
> i = current->task_isol_info;
> if (i->active_mask != ISOL_F_QUIESCE)
> return 0;
>
> if (!(i->quiesce_mask & ISOL_F_QUIESCE_VMSTATS))
> return 0;
>
> cpu = get_cpu();
> ret = per_cpu(vmstat_dirty, cpu);
> put_cpu();
>
> return ret;
> }
>
> Well, whether its necessary to call task_isol_exit_to_user_mode depends
> on the state of the enabled/disabled masks _and_ vmstat dirty bit
> information.
>
> It seems awkward, to me, to condense all that information in a single bit.
>
> Addressed all other comments, thanks.

You're unconditionally adding overhead to the syscall fastpath when it would
be so easy to set a TIF_FLAG as long as (current->task_isol_info->quiesce_mask
!= 0). vmstat_dirty can be checked afterward.

I suspect your patchset will sell much better if you join the common slowpath
single condition in EXIT_TO_USER_MODE_WORK.

Thanks.

\
 
 \ /
  Last update: 2022-01-27 19:02    [W:0.126 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site