Re: [PATCH 1/1] Drivers: hv: vmbus: Limit channel interrupt scan to relid high water mark

[Wei Liu <wei.liu@kernel.org>]

On Fri, Feb 20, 2026 at 08:40:45AM -0800, Michael Kelley wrote:
> From: Michael Kelley <mhklinux@outlook.com>
> 
> When checking for VMBus channel interrutps, current code always scans the
> full SynIC receive interrupt bit array to get the relid of the
> interrupting channels. The array has HV_EVENT_FLAGS_COUNT (2048) bits.
> But VMs rarely have more than 100 channels, and the relid is typically
> a small integer that is densely assigned by the Hyper-V host. It's
> wasteful to scan 2048 bits when it is highly unlikely that anything will
> be found past bit 100. The waste is double with Confidential VMBus because
> there are two receive interrupt arrays that must be scanned: one for the
> hypervisor SynIC and one for the paravisor SynIC.
> 
> Improve the scanning by tracking the largest relid that has been offered
> by the Hyper-V host. Then when checking for VMBus channel interrupts, only
> scan up to this high water mark.
> 
> When channels are rescinded, it's not worth the complexity to recalculate
> the high water mark. Hyper-V tends to reuse the rescinded relids for any
> new channels that are subsequently added, and the performance benefit of
> exactly tracking the high water mark would be minimal.
> 
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>

Applied to hyperv-next. Thanks.