Re: [RFC PATCH 1/3] irqchip/gic-v3: Make use of ICC_SGI1R IRM bit
From: Marc Zyngier <maz@kernel.org>
Date: 2021-03-29 11:29:45
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On Mon, 29 Mar 2021 11:38:04 +0100, Jingyi Wang [off-list ref] wrote:
On 3/29/2021 5:55 PM, Marc Zyngier wrote:quoted
On Mon, 29 Mar 2021 09:52:08 +0100, Jingyi Wang [off-list ref] wrote:quoted
IRM, bit[40] in ICC_SGI1R, determines how the generated SGIs are distributed to PEs. If the bit is set, interrupts are routed to all PEs in the system excluding "self". We use cpumask to determine if this bit should be set and make use of that. This will reduce vm trap when broadcast IPIs are sent.I remember writing similar code about 4 years ago, only to realise what: - the cost of computing the resulting mask is pretty high for large machines - Linux almost never sends broadcast IPIs, so the complexity was all in vain What changed? Please provide supporting data showing how many IPIs we actually save, and for which workload.Maybe we can implement send_IPI_allbutself hooks as other some other archs instead of computing cpumask here?
The question remains: how often is that used? x86 uses it only for NMI (we don't broadcast our pseudo-NMI) and reboot, it seems. Anything I missed? Do we have a different use case on arm64? At the moment, this doesn't seem very useful. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel