Re: [PATCH v2 14/35] PCI: hv: switch hv_get_dom_num() to use atomic find_bit()

Bjorn Helgaas
2023-12-04T19:14:34Z

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@google.com>

> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> Reviewed-by: Michael Kelley <mhklinux@outlook.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
>