Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.38 as permitted sender) client-ip=23.128.96.38;
From:   David Laight <David.Laight@ACULAB.COM>
To:     'James Morse' <james.morse@arm.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Babu Moger <Babu.Moger@amd.com>,
        "shameerali.kolothum.thodi@huawei.com" 
        <shameerali.kolothum.thodi@huawei.com>,
        D Scott Phillips OS <scott@os.amperecomputing.com>,
        "carl@os.amperecomputing.com" <carl@os.amperecomputing.com>,
        "lcherian@marvell.com" <lcherian@marvell.com>,
        "bobo.shaobowang@huawei.com" <bobo.shaobowang@huawei.com>,
        "tan.shaopeng@fujitsu.com" <tan.shaopeng@fujitsu.com>,
        "xingxin.hx@openanolis.org" <xingxin.hx@openanolis.org>,
        "baolin.wang@linux.alibaba.com" <baolin.wang@linux.alibaba.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Xin Hao <xhao@linux.alibaba.com>,
        "peternewman@google.com" <peternewman@google.com>,
        "dfustini@baylibre.com" <dfustini@baylibre.com>,
        "amitsinght@marvell.com" <amitsinght@marvell.com>
Subject: RE: [PATCH v6 09/24] x86/resctrl: Use set_bit()/clear_bit() instead
 of open coding
Thread-Topic: [PATCH v6 09/24] x86/resctrl: Use set_bit()/clear_bit() instead
 of open coding
Thread-Index: AQHZ5zAaDgmrK1w/n0WuE13QIAvATLAfhSSQ
Date:   Sun, 17 Sep 2023 21:00:40 +0000
Message-ID: <6f7b411db77846b2a305b93d0cf0ee7b@AcuMS.aculab.com>
References: <20230914172138.11977-1-james.morse@arm.com>
 <20230914172138.11977-10-james.morse@arm.com>
In-Reply-To: <20230914172138.11977-10-james.morse@arm.com>
Accept-Language: en-GB, en-US
MIME-Version: 1.0
Content-Language: en-US
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Precedence: bulk

From: James Morse
> Sent: 14 September 2023 18:21
> 
> The resctrl CLOSID allocator uses a single 32bit word to track which
> CLOSID are free. The setting and clearing of bits is open coded.
> 
> A subsequent patch adds resctrl_closid_is_free(), which adds more open
> coded bitmaps operations. These will eventually need changing to use
> the bitops helpers so that a CLOSID bitmap of the correct size can be
> allocated dynamically.
> 
> Convert the existing open coded bit manipulations of closid_free_map
> to use set_bit() and friends.
> 
>  int closids_supported(void)
> @@ -126,7 +126,7 @@ static void closid_init(void)
>  	closid_free_map = BIT_MASK(rdt_min_closid) - 1;
> 
>  	/* CLOSID 0 is always reserved for the default group */
> -	closid_free_map &= ~1;
> +	clear_bit(0, &closid_free_map);

Don't the clear_bit() etc functions use locked accesses?
These are always measurably more expensive than the C operators.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)