lkml.org 
[lkml]   [2020]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH V7 4/4] softirq: Allow early break the softirq processing loop
On Thu, Sep 24, 2020 at 05:37:42PM +0200, Thomas Gleixner wrote:
> Subject: softirq; Prevent starvation of higher softirq vectors
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Thu, 24 Sep 2020 10:40:24 +0200
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> The early termination of the softirq processing loop can lead to starvation
> of the higher numbered soft interrupt vectors because each run starts at
> the lowest bit. If the loop terminates then the already processed bits can
> be raised again before the next loop starts. If these lower bits run into
> the termination again, then a re-raise might starve the higher bits forever.
>
> To prevent this, store the leftovers of the previous run in the upper 16
> bit of the local softirq_pending storage and ensure that these are
> processed before any newly raised bits are handled.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> kernel/softirq.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 50 insertions(+), 8 deletions(-)
>
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -259,11 +259,23 @@ static inline bool __softirq_needs_break
> return need_resched() || __softirq_timeout(tbreak);
> }
>
> +/*
> + * local_softirq_pending() is split into two 16 bit words. The low word
> + * contains the bits set by raise_softirq(), the high word contains pending
> + * bits which have not been processed in an early terminated run. This is
> + * required to prevent starvation of the higher numbered softirqs.
> + */
> +#define SIRQ_PREV_SHIFT 16

Note that in the case of x86, irq_start.__softirq_pending is a u16.

The origin is there: 9aee5f8a7e30330d0a8f4c626dc924ca5590aba5
"x86/irq: Demote irq_cpustat_t::__softirq_pending to u16"

\
 
 \ /
  Last update: 2020-09-25 01:09    [W:0.076 / U:1.360 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site