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From: "Jan Beulich" <JBeulich@suse.com>
To: Chao Gao <chao.gao@intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	xen-devel@lists.xen.org
Subject: Re: [PATCH v5 3/4] VT-d PI: restrict the number of vcpus in a given pcpu's PI blocking list
Date: Thu, 31 Aug 2017 10:01:56 -0600	[thread overview]
Message-ID: <59A84F14020000780017640A@prv-mh.provo.novell.com> (raw)
In-Reply-To: <1502860478-84512-4-git-send-email-chao.gao@intel.com>

>>> On 16.08.17 at 07:14, <chao.gao@intel.com> wrote:
> +static inline bool pi_over_limit(unsigned int cpu)
> +{
> +    /* Compare w/ constant first to save a division and an add */
> +    if ( likely(read_atomic(&per_cpu(vmx_pi_blocking, cpu).counter) <=
> +                PI_LIST_FIXED_LIMIT) )
> +        return 0;

false

> +    else

Pointless else.

> +static unsigned int pi_get_blocking_cpu(unsigned int cpu, unsigned long *flags)
> +{
> +    spinlock_t *pi_blocking_list_lock;
> +
> +    for ( ; ; )
> +    {
> +        while ( unlikely(pi_over_limit(cpu)) )
> +            cpu = cpumask_cycle(cpu, &cpu_online_map);
> +
> +        pi_blocking_list_lock = &per_cpu(vmx_pi_blocking, cpu).lock;
> +        if ( flags )
> +            spin_lock_irqsave(pi_blocking_list_lock, *flags);
> +        else
> +            spin_lock(pi_blocking_list_lock);

This is ugly, but I think I see why you want it this way. Let's see
what the maintainers think.

Jan


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  reply	other threads:[~2017-08-31 16:01 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-16  5:14 [PATCH v5 0/4] mitigate the per-pCPU blocking list may be too long Chao Gao
2017-08-16  5:14 ` [PATCH v5 1/4] VT-d PI: track the number of vcpus on pi blocking list Chao Gao
2017-08-30 16:00   ` Jan Beulich
2017-08-30 22:57     ` Chao Gao
2017-08-31  7:42       ` Jan Beulich
2017-08-31  7:15         ` Chao Gao
2017-08-31  8:33           ` Jan Beulich
2017-08-31  7:53             ` Chao Gao
2017-09-01  1:39             ` Chao Gao
2017-09-01  8:24               ` Jan Beulich
2017-09-01  7:55                 ` Chao Gao
2017-09-01  9:13                   ` Jan Beulich
2017-09-01  8:37                     ` Chao Gao
2017-09-01  9:55                       ` Jan Beulich
2017-09-01 10:04                         ` Jan Beulich
2017-08-16  5:14 ` [PATCH v5 2/4] x86/vcpu: track hvm vcpu number on the system Chao Gao
2017-08-16  5:14 ` [PATCH v5 3/4] VT-d PI: restrict the number of vcpus in a given pcpu's PI blocking list Chao Gao
2017-08-31 16:01   ` Jan Beulich [this message]
2017-08-16  5:14 ` [PATCH v5 4/4] xentrace: add support for HVM's PI blocking list operation Chao Gao

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