On Tue, 2 Jul 2019 21:58:40 +0300 Ivan Khoronzhuk <[email protected]> wrote:
> On Tue, Jul 02, 2019 at 08:29:07PM +0200, Jesper Dangaard Brouer wrote: > >On Tue, 2 Jul 2019 18:21:13 +0300 > >Ivan Khoronzhuk <[email protected]> wrote: > > > >> On Tue, Jul 02, 2019 at 05:10:29PM +0200, Jesper Dangaard Brouer wrote: > >> >On Tue, 2 Jul 2019 17:56:13 +0300 > >> >Ivan Khoronzhuk <[email protected]> wrote: > >> > > >> >> On Tue, Jul 02, 2019 at 04:52:30PM +0200, Jesper Dangaard Brouer wrote: > >> >> > >> >> >On Tue, 2 Jul 2019 17:44:27 +0300 > >> >> >Ivan Khoronzhuk <[email protected]> wrote: > >> >> > > >> >> >> On Tue, Jul 02, 2019 at 04:31:39PM +0200, Jesper Dangaard Brouer > >> >> >> wrote: > >> >> >> >From: Ivan Khoronzhuk <[email protected]> > >> >> >> > > >> >> >> >Jesper recently removed page_pool_destroy() (from driver > >> >> >> >invocation) and > >> >> >> >moved shutdown and free of page_pool into xdp_rxq_info_unreg(), > >> >> >> >in-order to > >> >> >> >handle in-flight packets/pages. This created an asymmetry in drivers > >> >> >> >create/destroy pairs. > >> >> >> > > >> >> >> >This patch add page_pool user refcnt and reintroduce > >> >> >> >page_pool_destroy. > >> >> >> >This serves two purposes, (1) simplify drivers error handling as > >> >> >> >driver now > >> >> >> >drivers always calls page_pool_destroy() and don't need to track if > >> >> >> >xdp_rxq_info_reg_mem_model() was unsuccessful. (2) allow special > >> >> >> >cases > >> >> >> >where a single RX-queue (with a single page_pool) provides packets > >> >> >> >for two > >> >> >> >net_device'es, and thus needs to register the same page_pool twice > >> >> >> >with two > >> >> >> >xdp_rxq_info structures. > >> >> >> > >> >> >> As I tend to use xdp level patch there is no more reason to mention > >> >> >> (2) case > >> >> >> here. XDP patch serves it better and can prevent not only obj > >> >> >> deletion but also > >> >> >> pool flush, so, this one patch I could better leave only for (1) > >> >> >> case. > >> >> > > >> >> >I don't understand what you are saying. > >> >> > > >> >> >Do you approve this patch, or do you reject this patch? > >> >> > > >> >> It's not reject, it's proposition to use both, XDP and page pool > >> >> patches, > >> >> each having its goal. > >> > > >> >Just to be clear, if you want this patch to get accepted you have to > >> >reply with your Signed-off-by (as I wrote). > >> > > >> >Maybe we should discuss it in another thread, about why you want two > >> >solutions to the same problem. > >> > >> If it solves same problem I propose to reject this one and use this: > >> https://lkml.org/lkml/2019/7/2/651 > > > >No, I propose using this one, and rejecting the other one. > > There is at least several arguments against this one (related (2) purpose) > > It allows: > - avoid changes to page_pool/mlx5/netsec > - save not only allocator obj but allocator "page/buffer flush" > - buffer flush can be present not only in page_pool but for other allocators > that can behave differently and not so simple solution. > - to not limit cpsw/(potentially others) to use "page_pool" allocator only > .... > > This patch better leave also, as it simplifies error path for page_pool and > have more error prone usage comparing with existent one. > > Please, don't limit cpsw and potentially other drivers to use only > page_pool it can be zca or etc... I don't won't to modify each allocator. > I propose to add both as by fact they solve different problems with common > solution. I'm trying to limit the scope of your changes, for your special case, because I'm afraid this more common solution is going to limit our options, painting ourselves into a corner. E.g. for correct lifetime handling, I think we actually need to do a dev_hold() on the net_device. (Changes in f71fec47c2 might not be enough, but I first need to dig into the details and ask Hellwig about some details). Adding that after your patch is more complicated (if even doable). E.g. doing dev_hold() on the net_device, can also turn into a performance advantage, when/if page_pool is extended to also "travel" into SKBs. (Allowing to elide such dev_hold() calls in netstack). I also worry about the possible performance impact these changes will have down the road. (For the RX/alloc side it should be clear by now that we gain a lot of performance with the single RX-queue binding and napi protection). On the return/free side performance *need* to be improved (it doesn't scale). I'm basically looking at different ways to bulk return pages into the ptr_ring, which requires changes in page_pool and likely in xdp_allocator structure. Which your changes are complicating. This special use-case, seems confined to your driver. And Ilias told me that XDP is not really a performance benefit for this driver as the HW PPS-limit is hit before the XDP and netstack limit. I ask, does it make sense to add XDP to this driver, if it complicates the code for everybody else? -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
