[CRIU] [PATCH 7/8] sig: Optimize sigactions restore

[Andrew Vagin]

On Wed, Aug 06, 2014 at 04:25:38PM +0400, Pavel Emelyanov wrote:
> Most of the sigactions are the same across the tasks in the image.
> Nonetheless existing code always calls a syscall to restore them 
> and spends 64 calls per-task.
> 
> Let's restore signals before forking children and let them inherit
> sigactions. Tune one only if it differs from the parent's.

I like the idea. Do we have test, which uses different signal actions
for parent and child?

> 
> Signed-off-by: Pavel Emelyanov <xemul at parallels.com>
> ---
>  cr-restore.c | 32 ++++++++++++++++++++++++++++----
>  1 file changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/cr-restore.c b/cr-restore.c
> index afdafd8..0408aa3 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -614,6 +614,22 @@ static int open_vmas(int pid)
>  }
>  
>  static rt_sigaction_t sigchld_act;
> +static rt_sigaction_t parent_act[SIGMAX];
> +
> +static bool sa_inherited(int sig, rt_sigaction_t *sa)
> +{
> +	rt_sigaction_t *pa;
> +
> +	if (current == root_item)
> +		return false; /* XXX -- inherit from CRIU? */
> +
> +	pa = &parent_act[sig];
> +	return pa->rt_sa_handler == sa->rt_sa_handler &&
> +		pa->rt_sa_flags == sa->rt_sa_flags &&
> +		pa->rt_sa_restorer == sa->rt_sa_restorer &&
> +		pa->rt_sa_mask.sig[0] == sa->rt_sa_mask.sig[0];
> +}
> +
>  static int prepare_sigactions(void)
>  {
>  	int pid = current->pid.virt;
> @@ -621,7 +637,7 @@ static int prepare_sigactions(void)
>  	int fd_sigact;
>  	SaEntry *e;
>  	int sig;
> -	int ret = -1;
> +	int ret = 0;
>  
>  	fd_sigact = open_image(CR_FD_SIGACT, O_RSTR, pid);
>  	if (fd_sigact < 0)
> @@ -655,6 +671,10 @@ static int prepare_sigactions(void)
>  			sigchld_act = act;
>  			continue;
>  		}
> +
> +		if (sa_inherited(sig, &act))
> +			continue;
> +
>  		/*
>  		 * A pure syscall is used, because glibc
>  		 * sigaction overwrites se_restorer.
> @@ -664,6 +684,8 @@ static int prepare_sigactions(void)
>  			pr_err("%d: Can't restore sigaction: %m\n", pid);
>  			goto err;
>  		}
> +
> +		parent_act[sig] = act;
>  	}
>  
>  err:
> @@ -716,9 +738,6 @@ static int restore_one_alive_task(int pid, CoreEntry *core)
>  	if (prepare_file_locks(pid))
>  		return -1;
>  
> -	if (prepare_sigactions())
> -		return -1;
> -
>  	if (open_vmas(pid))
>  		return -1;
>  
> @@ -1346,6 +1367,9 @@ static int restore_task_with_children(void *_arg)
>  	if (prepare_task_cgroup(current) < 0)
>  		return -1;
>  
> +	if (prepare_sigactions() < 0)
> +		return -1;
> +
>  	if (create_children_and_session())
>  		goto err;
>  
> -- 
> 1.8.4.2
> 
> 
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