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Tsirkin" , Cornelia Huck , Halil Pasic Subject: Re: [PATCH v1 07/14] s390x/s390-hypercall: introduce DIAG500 STORAGE_LIMIT Message-ID: <20241001153132.08b0dca9.pasic@linux.ibm.com> In-Reply-To: <972044f1-62e4-4ac0-8b24-e0bb78770309@linux.ibm.com> References: <20240910175809.2135596-1-david@redhat.com> <20240910175809.2135596-8-david@redhat.com> <6636c963-228f-4bea-87c5-bd4f75521c75@redhat.com> <20240927200525.5a90f172.pasic@linux.ibm.com> <10165d22-c3e8-4db1-9874-8b63ca59afe9@linux.ibm.com> <20240930145712.526a1c79.pasic@linux.ibm.com> <972044f1-62e4-4ac0-8b24-e0bb78770309@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: YD0iDV6GFGEJoQVXxgep0y-yVGcVseEe X-Proofpoint-GUID: Pc_q931itZ8Div3LZoIGkwSqd3n1Xv4u X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-01_09,2024-09-30_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 phishscore=0 adultscore=0 mlxlogscore=735 suspectscore=0 malwarescore=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2408220000 definitions=main-2410010084 Received-SPF: pass client-ip=148.163.156.1; envelope-from=pasic@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, 1 Oct 2024 11:15:02 +0200 Christian Borntraeger wrote: [..] > >> So 500+4 should probably not cause any harm apart from branch prediction > >> going wrong the first 2 or 3 notifies. > >> > >> 502 will make kvm_s390_handle_diag larger. > > > > What do you mean by this last paragraph? [..] > gcc has logic for switch statements that decide about branch table or > a chained compare+jump. I think due to spectre gcc now avoids indirect > branches as much as possible but still a larger switch statement might > kick the decision from inline compare/jump to a branch table. > > I am not worried in this particular case this was more or less a > "what could go wrong". Hm, you did state that "502 will make kvm_s390_handle_diag larger". I suppose now we agree that 502 would not make kvm_s390_handle_diag larger. Right? I understood that you prefer 500+4 over 502 because the latter would make kvm_s390_handle_diag larger. Now that we have, I hope clarified, that 502 would not make the switch larger, do you still prefer 500+4? BTW your insights are very appreciated! Regards, Halil