Messages in this thread | | | Date | Fri, 16 Feb 2024 15:25:04 +0100 | From | Wenjia Zhang <> | Subject | Re: [PATCH net-next 13/15] net/smc: introduce loopback-ism DMB type control |
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On 11.01.24 13:00, Wen Gu wrote: > This provides a way to {get|set} type of DMB offered by loopback-ism, > whether it is physically or virtually contiguous memory. > > echo 0 > /sys/devices/virtual/smc/loopback-ism/dmb_type # physically > echo 1 > /sys/devices/virtual/smc/loopback-ism/dmb_type # virtually > > The settings take effect after re-activating loopback-ism by: > > echo 0 > /sys/devices/virtual/smc/loopback-ism/active > echo 1 > /sys/devices/virtual/smc/loopback-ism/active > > After this, the link group and DMBs related to loopback-ism will be > flushed and subsequent DMBs created will be of the desired type. > > The motivation of this control is that physically contiguous DMB has > best performance but is usually expensive, while the virtually > contiguous DMB is cheap and perform well in most scenarios, but if > sndbuf and DMB are merged, virtual DMB will be accessed concurrently > in Tx and Rx and there will be a bottleneck caused by lock contention > of find_vmap_area when there are many CPUs and CONFIG_HARDENED_USERCOPY > is set (see link below). So an option is provided. > I'm courious about why you say that physically contiguous DMB has best performance. Because we saw even a bit better perfomance with the virtual one than the performance with the physical one.
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