On Thu, Dec 10, 2015 at 5:20 PM, Haggai Eran <hagg...@mellanox.com> wrote: > On 10/12/2015 16:59, Matan Barak wrote: >> On Mon, Dec 7, 2015 at 3:18 PM, Haggai Eran <hagg...@mellanox.com> wrote: >>> On 12/03/2015 05:44 PM, Matan Barak wrote: >>>> Extending core and vendor verb commands require us to check that the >>>> unknown part of the user's given command is all zeros. >>>> Adding ib_is_udata_cleared in order to do so. >>>> >>> >>> Why not copy the data into kernel space and run memchr_inv() on it? >>> >> >> Probably less efficient, isn't it? > Why do you think it is less efficient? > > I'm not sure calling copy_from_user multiple times is very efficient. > For once, you are calling access_ok multiple times. I guess it depends > on the amount of data you are copying. >
Isn't access_ok pretty cheap? It calls __chk_range_not_ok which on x86 seems like a very cheap function and __chk_user_ptr which is a compiler check. I guess most kernel-user implementation will be pretty much in sync, so we'll possibly call it for a few/dozens of bytes. In that case, I think this implementation is a bit faster. >> I know it isn't data path, but we'll execute this code in all extended >> functions (sometimes even more than once). > Do you think it is important enough to maintain our own copy of > memchr_inv()? > True, I'm not sure it's important enough, but do you think it's that complicated? -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
