Messages in this thread | | | Date | Fri, 24 Sep 2021 11:55:32 +0530 | From | jeyr@codeauro ... | Subject | Re: [PATCH] misc: fastrpc: copy to user only for non-DMA-BUF heap buffers |
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On 2021-09-23 23:13, Greg KH wrote: > On Thu, Sep 23, 2021 at 03:54:15PM +0530, jeyr@codeaurora.org wrote: >> On 2021-09-23 14:19, Greg KH wrote: >> > On Thu, Sep 23, 2021 at 02:07:52PM +0530, Jeya R wrote: >> > > fastrpc_put_args is copying all the output buffers to user. For large >> > > number of output context buffers, this might cause performance >> > > degradation. Copying is not needed for DMA-BUF heap buffers. >> > >> > What does "performance degradation" really mean? >> >> Unnecessary copying for large number of buffers would cause some >> additional time which would get added to overall fastrpc call cost. >> >> > >> > > >> > > Signed-off-by: Jeya R <jeyr@codeaurora.org> >> > > --- >> > > drivers/misc/fastrpc.c | 18 ++++++++++-------- >> > > 1 file changed, 10 insertions(+), 8 deletions(-) >> > > >> > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c >> > > index beda610..536eabf 100644 >> > > --- a/drivers/misc/fastrpc.c >> > > +++ b/drivers/misc/fastrpc.c >> > > @@ -890,15 +890,17 @@ static int fastrpc_put_args(struct >> > > fastrpc_invoke_ctx *ctx, >> > > inbufs = REMOTE_SCALARS_INBUFS(ctx->sc); >> > > >> > > for (i = inbufs; i < ctx->nbufs; ++i) { >> > > - void *src = (void *)(uintptr_t)rpra[i].pv; >> > > - void *dst = (void *)(uintptr_t)ctx->args[i].ptr; >> > > - u64 len = rpra[i].len; >> > > + if (!ctx->maps[i]) { >> > > + void *src = (void *)(uintptr_t)rpra[i].pv; >> > > + void *dst = (void *)(uintptr_t)ctx->args[i].ptr; >> > >> > uintptr_t is not a kernel variable type. Please use the real kernel >> > type for this as you are touching these lines. >> > >> >> Sure, thanks for pointing this. Will update this in the next patch. >> >> > > + u64 len = rpra[i].len; >> > > >> > > - if (!kernel) { >> > > - if (copy_to_user((void __user *)dst, src, len)) >> > > - return -EFAULT; >> > > - } else { >> > > - memcpy(dst, src, len); >> > > + if (!kernel) { >> > > + if (copy_to_user((void __user *)dst, src, len)) >> > > + return -EFAULT; >> > > + } else { >> > > + memcpy(dst, src, len); >> > > + } >> > >> > So you were copying buffers that didn't need to be copied? So you are >> > now doing less work? Or is this fixing a bug where you were copying >> > things that you should not have been copying? >> > >> > What commit does this fix? Does this need to go to the stable kernel >> > trees? >> > >> >> Yes, not all buffer needs to be copied. This change would avoid >> unnecessary >> copying of buffers. Not adding fix tag as it's not exactly fixing any >> bug. >> This should go to stable kernel trees. > > If it's not fixing a bug, why should it go into the stable trees?
This is not a bug fix, it can be considered as an enhancement and it can go in to new release.
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