From mboxrd@z Thu Jan 1 00:00:00 1970 From: Helge Deller Subject: Re: CONFIG_XPS depends on L1_CACHE_BYTES being greater than sizeof(struct xps_map) Date: Sat, 24 Oct 2015 00:17:36 +0200 Message-ID: <562AB200.8030209@gmx.de> References: <32A3BF6F-B243-4AD4-9AE9-A5F9DAE0270A@bell.net> <1445524549.2207.1.camel@HansenPartnership.com> <5628F868.3040105@bell.net> <5629404B.8090805@gmx.de> <1445550615.22974.128.camel@edumazet-glaptop2.roam.corp.google.com> <562A8990.9000808@gmx.de> <1445630588.22974.187.camel@edumazet-glaptop2.roam.corp.google.com> <20151023210810.GA1969@ls3530.box> <562AAE05.5020300@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Tom Herbert , "David S. Miller" , netdev@vger.kernel.org To: Alexander Duyck , Eric Dumazet , linux-parisc@vger.kernel.org, James Bottomley , John David Anglin Return-path: In-Reply-To: <562AAE05.5020300@gmail.com> Sender: linux-parisc-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 24.10.2015 00:00, Alexander Duyck wrote: > On 10/23/2015 02:08 PM, Helge Deller wrote: >> * Eric Dumazet : >>> On Fri, 2015-10-23 at 21:25 +0200, Helge Deller wrote: >>> >>>> Then, how about simply changing it to twice of L1_CACHE_BYTES ? >>>> >>>> #define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES * 2 - sizeof(struct xps_map)) / sizeof(u16)) >>> >>> >>> Seems good to me. >> >> Great! >> >> Can you then maybe give me an Acked-by or signed-off for the patch below? >> It further adds a compile-time check to avoid that XPS_MIN_MAP_ALLOC >> gets calculated to zero on any architecture - otherwise no queues would >> be allocated. >> >> In addition I would like to push it for v4.3 then through my parisc-tree >> (after keeping it in for-next for 1-2 days), together with the patch >> which reduces L1_CACHE_BYTES to 16 on parisc. >> Would that be OK too? >> >> Thanks! >> Helge >> >> >> [PATCH] net/xps: Increase initial number of xps queues >> >> Increase the number of initial allocated xps queues, so that the initial record >> allocates twice the size of L1_CACHE_BYTES bytes. >> >> This change is needed to copy with architectures where L1_CACHE_BYTES is >> defined to equal or less than 16 bytes. >> >> Signed-off-by: Helge Deller >> >> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h >> index 2d15e38..d152788 100644 >> --- a/include/linux/netdevice.h >> +++ b/include/linux/netdevice.h >> @@ -718,7 +718,7 @@ struct xps_map { >> u16 queues[0]; >> }; >> #define XPS_MAP_SIZE(_num) (sizeof(struct xps_map) + ((_num) * sizeof(u16))) >> -#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - sizeof(struct xps_map)) \ >> +#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES * 2 - sizeof(struct xps_map)) \ >> / sizeof(u16)) >> >> /* >> diff --git a/net/core/dev.c b/net/core/dev.c >> index 6bb6470..f6d6dd1 100644 >> --- a/net/core/dev.c >> +++ b/net/core/dev.c >> @@ -1972,6 +1972,8 @@ static struct xps_map *expand_xps_map(struct xps_map *map, >> int alloc_len = XPS_MIN_MAP_ALLOC; >> int i, pos; >> >> + BUILD_BUG_ON(XPS_MIN_MAP_ALLOC == 0); >> + >> for (pos = 0; map && pos < map->len; pos++) { >> if (map->queues[pos] != index) >> continue; >> >> > > Rather then leaving a potential bug you could probably rewrite the macro so that it will give you at least 1. > > All you need to do is something like the following > #define XPS_MIN_MAP_ALLOC \ > ((L1_CACHE_ALIGN(offsetof(struct xps_map, queue[1])) - \ > sizeof(struct xps_map)) / sizeof(u16)) > > That should give you at least an XPS_MIN_MAP_ALLOC of 1. Yes, good idea! What makes me wonder though (because I have no idea about the XPS code/layer): How likely is it, that more than 1 (e.g. minimum "X") queues are needed? E.g. if a typical system needs at least 3 queues, then doesn't it make sense to allocate at least 3 initially by using queue[3] in your proposed patch above ? What would "X" be then? Helge