Re: [Xen-devel] [PATCH v4 1/3] libxc: do some retries in xc_cpupool_removecpu() for EBUSY case

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 10, 2016 at 06:27:12AM +0100, Juergen Gross wrote:
> The hypervisor might return EBUSY when trying to remove a cpu from a
> cpupool when a domain running in this cpupool has pinned a vcpu
> temporarily. Do some retries in this case, perhaps the situation
> cleans up.
> 
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> ---
> V3: adjust coding style as requested by Wei Liu
> 
> V4: minor code modifications as suggested by Dario Faggioli
> ---
>  tools/libxc/xc_cpupool.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/libxc/xc_cpupool.c b/tools/libxc/xc_cpupool.c
> index c42273e..261b9c9 100644
> --- a/tools/libxc/xc_cpupool.c
> +++ b/tools/libxc/xc_cpupool.c
> @@ -20,6 +20,7 @@
>   */
>  
>  #include <stdarg.h>
> +#include <unistd.h>
>  #include "xc_private.h"
>  
>  static int do_sysctl_save(xc_interface *xch, struct xen_sysctl *sysctl)
> @@ -137,17 +138,34 @@ int xc_cpupool_addcpu(xc_interface *xch,
>      return do_sysctl_save(xch, &sysctl);
>  }
>  
> +/*
> + * The hypervisor might return EBUSY when trying to remove a cpu from a
> + * cpupool when a domain running in this cpupool has pinned a vcpu
> + * temporarily. Do some retries in this case, perhaps the situation
> + * cleans up.
> + */
> +#define NUM_RMCPU_BUSY_RETRIES 5
> +
>  int xc_cpupool_removecpu(xc_interface *xch,
>                           uint32_t poolid,
>                           int cpu)
>  {
> +    unsigned retries;
> +    int err;
>      DECLARE_SYSCTL;
>  
>      sysctl.cmd = XEN_SYSCTL_cpupool_op;
>      sysctl.u.cpupool_op.op = XEN_SYSCTL_CPUPOOL_OP_RMCPU;
>      sysctl.u.cpupool_op.cpupool_id = poolid;
>      sysctl.u.cpupool_op.cpu = (cpu < 0) ? XEN_SYSCTL_CPUPOOL_PAR_ANY : cpu;
> -    return do_sysctl_save(xch, &sysctl);
> +    for ( retries = 0; retries < NUM_RMCPU_BUSY_RETRIES; retries++ ) {
> +        err = do_sysctl_save(xch, &sysctl);
> +        if ( err < 0 && errno == EBUSY )
> +            sleep(1);
> +        else
> +            break;
> +    }
> +    return err;
>  }
>  
>  int xc_cpupool_movedomain(xc_interface *xch,
> -- 
> 2.6.2
> 

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