Re: [PATCH 2/4] hw/nvme: add option to (de)assert irq with eventfd

[Klaus Jensen <its@irrelevant.dk>]

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On Aug 11 23:37, Jinhao Fan wrote:
> When the new option 'irq-eventfd' is turned on, the IO emulation code
> signals an eventfd when it want to (de)assert an irq. The main loop
> eventfd handler does the actual irq (de)assertion.  This paves the way
> for iothread support since QEMU's interrupt emulation is not thread
> safe.
> 
> Asserting and deasseting irq with eventfd has some performance
> implications. For small queue depth it increases request latency but
> for large queue depth it effectively coalesces irqs.
> 
> Comparision (KIOPS):
> 
> QD            1   4  16  64
> QEMU         38 123 210 329
> irq-eventfd  32 106 240 364
> 
> Signed-off-by: Jinhao Fan <fanjinhao21s@ict.ac.cn>
> ---
>  hw/nvme/ctrl.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  hw/nvme/nvme.h |  4 +++
>  2 files changed, 90 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index bd3350d7e0..8a1c5ce3e1 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -7675,6 +7757,7 @@ static Property nvme_props[] = {
>      DEFINE_PROP_BOOL("use-intel-id", NvmeCtrl, params.use_intel_id, false),
>      DEFINE_PROP_BOOL("legacy-cmb", NvmeCtrl, params.legacy_cmb, false),
>      DEFINE_PROP_BOOL("ioeventfd", NvmeCtrl, params.ioeventfd, false),
> +    DEFINE_PROP_BOOL("irq-eventfd", NvmeCtrl, params.irq_eventfd, false),

This option does not seem to change anything - the value is never used
;)

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