lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Fri, 28 Jun 2019 18:11:54 -0600
From:   shuah <>
To:     Suwan Kim <>,,,
        shuah <>
Subject: Re: [PATCH 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

Hi Suwan,

On 6/21/19 11:45 AM, Suwan Kim wrote:
> vhci doesn’t do dma for remote device. Actually, the real dma
> operation is done by network card driver. So, vhci doesn’t use and
> need dma address of transfer buffer of urb.
> When vhci supports SG, it is useful to use native SG list instead
> of mapped SG list because dma mapping fnuction can adjust the
> number of SG list that is urb->num_mapped_sgs.
> But hcd provides dma mapping and unmapping function by defualt.

Typo "defualt"

> Moreover, it causes unnecessary dma mapping and unmapping which
> will be done again at the NIC driver and it wastes CPU cycles.
> So, implement map_urb_for_dma and unmap_urb_for_dma function for
> vhci in order to skip the dma mapping and unmapping procedure.

How did you verify that unnecessary dma map/unmap are happening?
How many CPU cycles did you manage to reduce with this change?

-- Shuah

Powered by blists - more mailing lists