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Message-ID: <ad917c1c-2508-41eb-ae5a-8b4fcd97ca7f@gmail.com>
Date: Sun, 11 May 2025 11:06:10 +0900
From: Daisuke Matsuda <dskmtsd@...il.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
leon@...nel.org, jgg@...pe.ca, zyjzyj2000@...il.com
Subject: Re: [PATCH for-next v2 1/2] RDMA/rxe: Implement synchronous prefetch
for ODP MRs
On 2025/05/10 17:04, Greg Sword wrote:
> On Sat, May 10, 2025 at 3:19 PM Daisuke Matsuda <dskmtsd@...il.com> wrote:
>>
>> On 2025/05/10 13:43, Zhu Yanjun wrote:
>>>
>>> 在 2025/5/10 4:46, Daisuke Matsuda 写道:
>>>> On 2025/05/10 0:19, Zhu Yanjun wrote:
>>>>> On 03.05.25 15:42, Daisuke Matsuda wrote:
>>>>>> Minimal implementation of ibv_advise_mr(3) requires synchronous calls being
>>>>>> successful with the IBV_ADVISE_MR_FLAG_FLUSH flag. Asynchronous requests,
>>>>>> which are best-effort, will be added subsequently.
>>>>>>
>>>>>> Signed-off-by: Daisuke Matsuda <dskmtsd@...il.com>
>>>>>> ---
>>>>>> drivers/infiniband/sw/rxe/rxe.c | 7 +++
>>>>>> drivers/infiniband/sw/rxe/rxe_loc.h | 10 ++++
>>>>>> drivers/infiniband/sw/rxe/rxe_odp.c | 86 +++++++++++++++++++++++++++++
>>>>>> 3 files changed, 103 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/infiniband/sw/rxe/rxe.c b/drivers/infiniband/sw/rxe/rxe.c
>>>>>> index 3a77d6db1720..e891199cbdef 100644
>>>>>> --- a/drivers/infiniband/sw/rxe/rxe.c
>>>>>> +++ b/drivers/infiniband/sw/rxe/rxe.c
>>>>>> @@ -34,6 +34,10 @@ void rxe_dealloc(struct ib_device *ib_dev)
>>>>>> mutex_destroy(&rxe->usdev_lock);
>>>>>> }
>>>>>> +static const struct ib_device_ops rxe_ib_dev_odp_ops = {
>>>>>> + .advise_mr = rxe_ib_advise_mr,
>>>>>> +};
>>>>>> +
>>>>>> /* initialize rxe device parameters */
>>>>>> static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>>>>> {
>>>>>> @@ -103,6 +107,9 @@ static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_SRQ_RECV;
>>>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_FLUSH;
>>>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_ATOMIC_WRITE;
>>>>>> +
>>>>>> + /* set handler for ODP prefetching API - ibv_advise_mr(3) */
>>>>>> + ib_set_device_ops(&rxe->ib_dev, &rxe_ib_dev_odp_ops);
>>>>>> }
>>>>>> }
>>>>>> diff --git a/drivers/infiniband/sw/rxe/rxe_loc.h b/drivers/infiniband/sw/rxe/rxe_loc.h
>>>>>> index f7dbb9cddd12..21b070f3dbb8 100644
>>>>>> --- a/drivers/infiniband/sw/rxe/rxe_loc.h
>>>>>> +++ b/drivers/infiniband/sw/rxe/rxe_loc.h
>>>>>> @@ -197,6 +197,9 @@ enum resp_states rxe_odp_atomic_op(struct rxe_mr *mr, u64 iova, int opcode,
>>>>>> int rxe_odp_flush_pmem_iova(struct rxe_mr *mr, u64 iova,
>>>>>> unsigned int length);
>>>>>> enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value);
>>>>>> +int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>>>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
>>>>>> + struct uverbs_attr_bundle *attrs);
>>>>>> #else /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>>>>> static inline int
>>>>>> rxe_odp_mr_init_user(struct rxe_dev *rxe, u64 start, u64 length, u64 iova,
>>>>>> @@ -225,6 +228,13 @@ static inline enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr,
>>>>>> {
>>>>>> return RESPST_ERR_UNSUPPORTED_OPCODE;
>>>>>> }
>>>>>> +static inline int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>>>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
>>>>>> + struct uverbs_attr_bundle *attrs)
>>>>>> +{
>>>>>> + return -EOPNOTSUPP;
>>>>>> +}
>>>>>> +
>>>>>> #endif /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>>>>> #endif /* RXE_LOC_H */
>>>>>> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
>>>>>> index 6149d9ffe7f7..e5c60b061d7e 100644
>>>>>> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
>>>>>> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
>>>>>> @@ -424,3 +424,89 @@ enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
>>>>>> return RESPST_NONE;
>>>>>> }
>>>>>> +
>>>>>> +static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
>>>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>>>> + u32 pf_flags, struct ib_sge *sg_list,
>>>>>> + u32 num_sge)
>>>>>> +{
>>>>>> + struct rxe_pd *pd = container_of(ibpd, struct rxe_pd, ibpd);
>>>>>> + unsigned int i;
>>>>>> + int ret = 0;
>>>>>> +
>>>>>> + for (i = 0; i < num_sge; ++i) {
>>>>>> + struct rxe_mr *mr;
>>>>>> + struct ib_umem_odp *umem_odp;
>>>>>> +
>>>>>> + mr = lookup_mr(pd, IB_ACCESS_LOCAL_WRITE,
>>>>>> + sg_list[i].lkey, RXE_LOOKUP_LOCAL);
>>>>>> +
>>>>>> + if (IS_ERR(mr)) {
>>>>>> + rxe_dbg_pd(pd, "mr with lkey %x not found\n", sg_list[i].lkey);
>>>>>> + return PTR_ERR(mr);
>>>>>> + }
>>>>>> +
>>>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>>>>>> + !mr->umem->writable) {
>>>>>> + rxe_dbg_mr(mr, "missing write permission\n");
>>>>>> + rxe_put(mr);
>>>>>> + return -EPERM;
>>>>>> + }
>>>>>> +
>>>>>> + ret = rxe_odp_do_pagefault_and_lock(mr, sg_list[i].addr,
>>>>>> + sg_list[i].length, pf_flags);
>>>>>> + if (ret < 0) {
>>>>>> + if (sg_list[i].length == 0)
>>>>>> + continue;
>>>>>> +
>>>>>> + rxe_dbg_mr(mr, "failed to prefetch the mr\n");
>>>>>> + rxe_put(mr);
>>>>>> + return ret;
>>>>>> + }
>>>>>> +
>>>>>> + umem_odp = to_ib_umem_odp(mr->umem);
>>>>>> + mutex_unlock(&umem_odp->umem_mutex);
>>>>>> +
>>>>>> + rxe_put(mr);
>>>>>> + }
>>>>>> +
>>>>>> + return 0;
>>>>>> +}
>>>>>> +
>>>>>> +static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
>>>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge)
>>>>>> +{
>>>>>> + u32 pf_flags = RXE_PAGEFAULT_DEFAULT;
>>>>>> +
>>>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH)
>>>>>> + pf_flags |= RXE_PAGEFAULT_RDONLY;
>>>>>> +
>>>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>>>>>> + pf_flags |= RXE_PAGEFAULT_SNAPSHOT;
>>>>>> +
>>>>>> + /* Synchronous call */
>>>>>> + if (flags & IB_UVERBS_ADVISE_MR_FLAG_FLUSH)
>>>>>> + return rxe_ib_prefetch_sg_list(ibpd, advice, pf_flags, sg_list,
>>>>>> + num_sge);
>>>>>> +
>>>>>> + /* Asynchronous call is "best-effort" */
>>>>>
>>>>> Asynchronous call is not implemented now, why does this comment appear?
>>>>
>>>> Even without the 2nd patch, async calls are reported as successful.
>>>
>>>
>>> Async call is not implemented. How to call "async calls are reported as successful"?
>>
>> Please see the manual.
>> cf. https://manpages.debian.org/testing/libibverbs-dev/ibv_advise_mr.3.en.html
>>
>> If IBV_ADVISE_MR_FLAG_FLUSH is not given to 'flags' parameter,
>> then this function 'rxe_ib_advise_mr_prefetch()' simply returns 0.
>> Consequently, ibv_advise_mr(3) and underlying ioctl(2) get no error.
>> This behaviour is allowd in the spec as I quoted in the last reply.
>
> The functionality wasn't implemented, you added the comments first.
> You're still weaseling when people point this out.
>
>>
>> It might be nice to return -EOPNOTSUPP just below the comment instead,
>> but not doing so is acceptable according to the spec. Additionally,
>> such change will be overwritten in the next patch after all.
>
> Move comments to the next patch. In this patch, return -EOPNOTSUPP.
Any opinion from Zhu?
I may post a new revision to change the intermediate code,
but the final result after applying the patchset will be the same.
You are the maintainer of rxe, so I will follow that.
Thanks,
Daisuke
>
> --G--
>
>>
>> Thanks,
>> Daisuke
>>
>>>
>>>
>>> Zhu Yanjun
>>>
>>>> The comment is inserted to show the reason, which is based on the
>>>> description from 'man 3 ibv_advise_mr' as follows:
>>>> ===
>>>> An application may pre-fetch any address range within an ODP MR when using the IBV_ADVISE_MR_ADVICE_PREFETCH or IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE advice. Semantically, this operation is best-effort. That means the kernel does not guarantee that underlying pages are updated in the HCA or the pre-fetched pages would remain resident.
>>>> ===
>>>>
>>>> Thanks,
>>>> Daisuke
>>>>
>>>>>
>>>>> Zhu Yanjun
>>>>>
>>>>>> +
>>>>>> + return 0;
>>>>>> +}
>>>>>> +
>>>>>> +int rxe_ib_advise_mr(struct ib_pd *ibpd,
>>>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>>>> + u32 flags,
>>>>>> + struct ib_sge *sg_list,
>>>>>> + u32 num_sge,
>>>>>> + struct uverbs_attr_bundle *attrs)
>>>>>> +{
>>>>>> + if (advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH &&
>>>>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>>>>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>>>>>> + return -EOPNOTSUPP;
>>>>>> +
>>>>>> + return rxe_ib_advise_mr_prefetch(ibpd, advice, flags,
>>>>>> + sg_list, num_sge);
>>>>>> +}
>>>>>
>>>>
>>
>>
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