linux-kernel - Re: [PATCH v2 14/35] PCI: hv: switch hv_get_dom_num() to use atomic find

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Date:   Mon, 4 Dec 2023 13:14:27 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v2 14/35] PCI: hv: switch hv_get_dom_num() to use atomic
 find_bit()

On Sun, Dec 03, 2023 at 11:32:46AM -0800, Yury Norov wrote:
> The function traverses bitmap with for_each_clear_bit() just to allocate
> a bit atomically. We can do it better with a dedicated find_and_set_bit().

No objection from me, but please tweak the subject line to match
previous hv history, i.e., capitalize the first word after the prefix:

  PCI: hv: Use atomic find_and_set_bit()

I think there's value in using similar phrasing across the whole
series.  Some subjects say "optimize xyz()", some say "rework xyz()",
some "rework xyz()", etc.  I think it's more informative to include
the "atomic" and "find_bit()" ideas in the subject than the specific
functions that *use* it.

I also like how some of the other commit logs clearly say what the
patch does, e.g., "Simplify by using dedicated find_and_set_bit()", as
opposed to just "We can do it better ..." which technically doesn't
say what the patch does.

Very nice simplification in all these users, thanks for doing it!

I assume you'll merge these all together since they depend on [01/35],
so:

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> Signed-off-by: Yury Norov <yury.norov@...il.com>
> Reviewed-by: Michael Kelley <mhklinux@...look.com>
> ---
>  drivers/pci/controller/pci-hyperv.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 30c7dfeccb16..033b1fb7f4eb 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -3605,12 +3605,9 @@ static u16 hv_get_dom_num(u16 dom)
>  	if (test_and_set_bit(dom, hvpci_dom_map) == 0)
>  		return dom;
>  
> -	for_each_clear_bit(i, hvpci_dom_map, HVPCI_DOM_MAP_SIZE) {
> -		if (test_and_set_bit(i, hvpci_dom_map) == 0)
> -			return i;
> -	}
> +	i = find_and_set_bit(hvpci_dom_map, HVPCI_DOM_MAP_SIZE);
>  
> -	return HVPCI_DOM_INVALID;
> +	return i < HVPCI_DOM_MAP_SIZE ? i : HVPCI_DOM_INVALID;
>  }
>  
>  /**
> -- 
> 2.40.1
>